
Spraying, or "urine-marking," is most common in cats that are not neutered or spayed, and typically occurs in homes with more than one cat. Spraying is a cat's way of claiming something as their own – much like children would, say, lick a piece of candy to claim it from his peers.
Usually spaying or neutering your pet will alleviate this problem. However, if there are other unfixed cats in your household, they may continue the behavior in reaction to them. It is highly recommended to spay and neuter your cats as early as possible to stop cat spraying before it becomes a habitual behavior.
There are several things you can do to help stop spraying:
Clean the soiled areas immediately and thoroughly. Cats will tend to spray in the same areas, so the goal here is to completely remove any trace of scent.
Move toys or other attractive items your cat was claiming by spraying to another area.
Make the marked territory inaccessible to your cat. If he can't get there, or it's covered up, he won't likely repeat the act.
Pet, talk nicely and play with him in the area where he tends to spray. This will calm him, and lessen the chances of needing to mark the area in the future.
Help him become better friends with other cats and pets in the house. Introduce them slowly and correctly to make the new company a smoother match.
At worst, you may need to get a professional cleaning of the area or re-carpet the often-marked area. While this is a bit of a bigger effort, doing so should throw off the cat's scent, and stop cat spraying in tougher to crack kitties.