Ugh, cat spraying. Spraying is not a litter box problem, but rather, is a behavior to mark territory. It is a communication system for cats, but not so cute on indoor walls and furniture.

To prevent spraying, you may wish to consult your vet about neutering your (male) cat and checking for possible medical causes. You can help by paying attention to the reasons he or she is spraying (yes, sometimes even females have this nasty habit).