Dog Rocks® are a product mined in Australia that helps prevent those nasty yellow urine burn stains appearing on your lawn. Dog Rocks® have been laboratory tested and is safe for your pet(s).With Dog Rocks the impurities, Tin, ammonia and nitrates, will be filtered out. These impurities are passed out through your dog's urine which causes dead, yellow patches on your lawn. So, adding a few Dog Rocks to your dog's water, your dog will have a cleaner source of water and will fertilize your lawn instead of burning it. .