Remember that the feline social system may also affect the behavior of a cat that is not using the litter box. Note any interactions that might be compounding the problem. All affected areas must be cleaned with an odor eliminator. After cleaning, cover affected areas with heavy-gauge plastic both to change the tactile sensation for the cat and to prevent further penetration in the event of elimination. Litter should be scooped daily, and most litters should be dumped totally every other day.
Many cats differ in their preference for litter depth.
Boxes should be washed weekly. Some old boxes may be so permeated with scent that they should be discarded. A variety of litters should be offered to the cat in a variety of boxes. Be creative and persistent. Consider trying one of the new trays where urine passes through rocks onto a pad below.