Why do cats spray and how do I get rid of that horrible smell?

Cats spray to mark their territory, one way to get them to stop spraying is to spay or neuter it. scrub with a hard bristle brush and a bucket of ammonia and water. let it air dry a bit and get some moth balls, crush them in a bag and sprinkle in the area. don't use more than one box of moth balls in one small area or your house will have a strong smell of moth balls