Also known as inappropriate elimination, there are 3 primary reasons why your cat may be avoiding or refusing to use the litterbox. A cat with this issue needs a veterinary examination to rule out medical causes first.
1. Medical Issues
Urinary tract infections, cystitis, bladder stones, diabetes, and kidney disease can cause increased and more frequent urination. Spinal arthritis, hip dysplasia or chronic constipation can also lead to inappropriate elimination.
Urine spraying, when a cat deposits urine on a vertical surface such as a wall, is the most common form of marking and is associated with a heightened state of emotional arousal or stress. Determine the cat’s triggers—a new cat in the household, changes in routine, aggression between cats, etc. Potential solutions involve removing or reducing the intensity of the identified triggers and providing plentiful resources for feeding, elimination, perching, scratching and playing, all of which should be tailored to your cat's social situation and personal preferences. Pheromone products and medications may also help. Your veterinarian can help you create a strategy to deal with marking behavior.
3. Toileting Problems
Toileting problems occur when a cat does not use the litterbox for its normal elimination. Typically, an owner will find urine and/or feces on a horizontal surface. This issue is often related to aversions—the cat may not like a dirty litterbox, the litter type, or the box size, style or location. Cat owners should have at least one litterbox per cat, plus one more. The boxes should be dispersed throughout the home. The boxes should be scooped daily and completely changed and washed regularly—the frequency will depend upon litter type, but this could range from weekly to monthly.
If a toileting problem is suspected, your veterinarian may recommend that you offer your cat various different litterbox setups to discover your cat's preferred toileting option(s). Most cats prefer a clay clumping litter in a large, open box. For certain cats, the litterboxes may need to be moved to a low-traffic/quiet area. If another cat or a dog is “guarding” the box, or if the cat feels like it’s too stressful getting to a box located in a busy area of the home, the cat may choose to go wherever it feels safe. You can also try putting a litterbox over the spot where the cat has been house-soiling. If you have senior cats, make sure the boxes are accessible. Low-sided boxes work best for cats with joint or arthritis issues.