Lawn Protector Pucks purify your pet’s drinking water and stops urine from damaging your lawn. Those ugly yellow patches in your grass, caused by your dog’s urine, can be expensive to repair. This safe, simple, and environmentally friendly solution to urine-burned lawn patches is delivered in the shape of a "hockey puck" in your pet’s water bowl or fountain. The nitrogen in your dog’s urine from the water he drinks causes his urine to become acidic. The water puck purifies your dog’s water by removing extra nitrogen, preventing the yellow patches from forming on your lawn.