Once your cat had an accident outside the litter box, preventing a repeat offense requires completely removing the cat urine odor. That can be hard to do because the cat can find very small amounts of cat urine you may not be able to detect. One trick you can use to make finding the cat urine easier is to shine a black UV light on the wall, flooring, or fabric. Cat urine glows under a black light. Then choose an "odor neutralizer" product, generally one that contains enzymes that actually digest the odor particles. A number of effective cat urine odor removal products are available from pet supply stores. Some cats will mark their territory by spraying. In addition to following the steps above to get rid of the odor, you may also want to consider the following: There are commercial spray products that use scent to help calm upset cat feelings. Ask about them at pet stores and veterinary offices. Facial pheromones - the scent cats leave behind when they cheek-rub objects - signal that everything is safe. The pheromone spray can be used on the "target" areas after you've removed the cat urine to help reduce the chance of a repeat offense. If you have more than one cat make sure that they each have one box they can claim as their own.