It’s a disappointment to find Pete Wedderburn, a qualified vet, endorsing “Dog Rocks”. Here’s what he printed in the Telegraph:

“The brown patches caused by dog urine on lawns are a perennial issue (to borrow a gardening term). Some people claim that a daily dollop of tomato ketchup in the dog’s dinner stops this but evidence is lacking. Dog Rocks are the most popular product marketed to help: these are placed in dogs’ water bowls, claiming to filter out excessive nitrogen and urea from the water. A high concentration of nitrates can cause grass to turn yellow or brown: the idea is that if less nitrates go into the dog, less come out the other end. Dog Rocks claim success in 80 per cent of cases when used according to instructions; they are widely available in pet shops and online (dogrocks.co.uk).”

It is amusing that Wedderburn dismisses ketchup as a solution for lawn burns on the basis of a lack of evidence and then recommends dog rocks instead, via an appeal to popularity. One might have thought that, given his science education, he would know that popularity isn’t evidence for efficacy. In his defence, he doesn’t explicitly claim that dog rocks work – he just says that the company does. Perhaps he simply assumed on good faith that a company claiming to have conducted laboratory tests on their product must be selling something legitimate – which is of course what we really ought to be able to assume, in an ideal world. Unfortunately, this world is not ideal.

According to the the company’s website, dog rocks are “an igneous Rock with absorbing & retaining qualities” that will “stop pet urine ruining your lawn, grass, shrubs and hedging”. The site offers no evidence to back up these claims, and is home to a plethora of archetypal pseudoscience – loose ideas arranged clumsily around science jargon like “stable matrix”, “micro porous medium”, “ion exchange” and “trace elements”. The marketers print the word “PROVEN” on their product packaging in big red capital letters and, as mentioned above, claim that their product is “laboratory tested”. But they fail to offer even the vaguest insight into the nature of these tests, providing no reference whatsoever to study design, who did the testing, or whether the research was published (or even written up), let alone quantitative information  like effect sizes, standard deviation, p-values, etc. Even anti-ageing face-cream companies manage to pay enough lip-service to transparency that we can go and see that their effects are based upon the subjective reports of 20 women brought into their own lab and not peer-reviewed.

Lack of peer-reviewed studies and misuse of science words are both pseudoscience red flags. Other red flags exhibited by the website are: a page of testimonials, repetitious appeals to nature (dog rocks are “100% natural!”), appeals to pH woo (dog rocks “do not change the pH balance of dog’s urine so they should not harm your dog at all”), and a sort of variation on the appeal to ancient wisdom – I’ll call it “provincial wisdom” (dog rocks were “discovered in Australia by an Aboriginal Gardener in the 1990s”).

A quick tour around the website confirms that discerning dog-owners most certainly are not this company’s target market, and makes it clear beyond any reasonable doubt that these “lab tests” are either irrelevant to the question of whether the product actually works, or simply non-existent. Here’s the “technical blurb” (that’s their term, by the way).

Dog Rocks are a coherent Rock with a mechanically stable framework meaning no significant mineral particles are released into the pet’s drinking water, in other words, Dog Rocks do not break down or leech anything into the pet’s drinking water. Dog Rocks form a stable matrix and a micro porous medium in which active components are able to act as a water-purifying agent through ion exchange. For this reason, when placed in water, Dog Rocks will help purify the water by removing some harmful trace elements giving your dog a cleaner source of water.

Perhaps it’s crude of me to even say this, but to my mind one of the most reliable indicators of junk science and B/S is simply the quality of writing. It doesn’t take a literary connoisseur to notice that the writing style exhibited on the Dog Rocks website is cringeworthily naff and unsophisticated, and it has what I would describe as an awkwardly ingratiating, cloying tone. Although that isn’t enough to dismiss scientific claims, in my experience, this particular form of prose is a strikingly accurate predictor of pseudoscience. Fortunately for our purposes, however, we have much more to sink our teeth into than that.

You might have noticed that no explanation is offered as to how the removal of “harmful trace elements” should result in a change in urine composition such that lawn burns would be prevented. Such ambiguous conflation of terms is yet another red flag: it’s not “harmful trace elements” that cause lawn burns, it’s urea and nitrates (both nitrogen-containing substances). This irrelevant appeal to TOXINS, TOXINS, EVERYWHERE and the promise to remove them seems to have been thrown in there opportunistically as a bonus selling point. You might also have noticed that ion-exchange is a two-way street, yet according to the distributors, nothing is released from the product into Buster’s water. Which is it, Dog Rocks?

I visited the FAQ section to find out more about how the product is supposed to work. Under the heading “How do DOG ROCKS work?”, the “technical blurb” quoted above is re-printed verbatim, except with a different incarnation of woofle following the phrase, “For this reason”:

For this reason, when placed in water, Dog Rocks will help purify the water by removing some nitrates, ammonia and harmful trace elements thereby giving your dog a cleaner source of water and lowering the amount of nitrates found in their diet thereby lowering the amount that is expelled in their urine. An overload of nitrates in urine will cause lawns to burn. Dogs do produce nitrates as a by-product from the protein in their diet, but the difference between too much nitrate that will kill the grass and the amount of nitrate that will be good for the grass is very small.

Carnivores have particularly high levels of nitrogen in their urine because their diets include so much protein, and the digestion of amino acids (the building blocks of protein) creates nitrogenous waste, primarily in the form of urea. As the above quote alludes to, diluted urine can be used as a fertiliser, precisely because it contains nitrogen – one of the most important macronutrients for plants. However, at high concentrations, it causes chemical burns to roots by sapping water from them as a result of osmotic pressure. Evidence that dog rocks can transform weedkiller-wee into fertilizer, as they claim, however, is entirely absent.

On the website, the manufacturers try to gloss over the fact that the nitrogen in dogs’ urine comes overwhelmingly from the protein that they eat with their assertion (featuring in the last quote) that “the difference between too much nitrate…and the amount…that will be good for the grass is very small”. The amount of urea in canine urine is 3.5 ± 2.4 mg/dl* – like human urine, it already varies quite considerably. The manufacturers are basically admitting that the reduction in nitrogen concentration achieved by dog rocks will be “very small”, but hanging on to the case for efficacy by saying that a very small reduction is all that is needed. Their use of the phrase “very small”, without any quantification or context is entirely unscientific and misleading. Small relative to what? An infinitesimal is “very small”; so is an electron; so is an ant; so is a Falabella pony, all relative to their contexts. 

The company fails to give a threshold concentration value of urinary nitrogen beyond which urine burns plant roots, and below which it doesn’t (which is fishy in and of itself – this would have been one of the most important things to determine in those “lab tests” they say they conducted). If the change in nitrogen concentration effected by dog rocks is “very small”, then the product should only work in the subset of cases in which a dog’s initial urinary nitrogen concentration happens to be just above this undeclared value, and for owners to notice a change would require that individual dogs always produced urine with that same concentration – just a “very small” fraction above the magic value – which they don’t. In reality, urea concentration fluctuates from pee to pee – the ability to vary urine concentration is one of the most important properties of the mammalian kidney. A “very small” change would would be drowned out by the noise of this daily variation. The only way I can see dog rocks working is if they were to effect a “very big” change which, given the relatively enormous amount of protein dogs eat, is physiologically implausible. So, assuming that dog rocks do actually remove nitrates from water (the website gives us no reason to believe that they do, and plenty of red flags to suggest that they probably don’t), the idea that this would translate into prevention of lawn burns in anywhere near 80% of cases is wholly unconvincing.

To summarise, the company has failed on four levels:

1) It provides no demonstration that the nitrates in the water a dog drinks contributes significantly towards its propensity to produce lawn spots.

2) It provides no evidence that dog rocks lower nitrate concentration in drinking water, nor does it describe a plausible mechanism for how they might do so, beyond unspecified “ion exchange”. (Incidentally, if these things really could absorb nitrates, wouldn’t the company be a major seller to people who own expensive aquarium set-ups?)

3) It provides no evidence, if indeed dietary nitrates consumed in water did play a significant role, that their product could significantly reduce nitrate content in dogs’ urine, relative to the nitrates coming from other sources (particularly the meat that they eat).

4) It provides no evidence that, if indeed their product did significantly reduce the nitrate content in dog urine relative to the nitrates coming from other sources, this would translate into an impact on lawn burn.