Dog Rocks help prevent those nasty yellow burn patches from appearing on your lawn. Completely natural and hassle free, simply place Dog Rocks in your dog's water dish and let them filter out impurities in the water such as tin, ammonia and nitrates. These impurities are usually passed out through urine, and when your grass comes in contact with these elements it is burned, resulting in a dead and yellow patch on your lawn. Without the impurities in the water, Dog Rocks actually help your dog fertilize your lawn. This is great for you, your dog & your lawn!