There are many reasons why cats do not use their litter box for urine, knowing why your cat is not using the litter box is very helpful when it comes to addressing, and fixing, the problem.
Take a Urine Sample to the Veterinarian
If you own a cat that is peeing around the home, you will need to collect a urine sample. In the afternoon confine your cat to a small room, or large dog kennel, and provide them an empty litter box. They should have food and water, but no bedding (or they may pee on the towels rather than in the box). In the morning they should have urinated in the litter box, using a clean syringe (you can get these at the veterinarian) suck up the urine. Either take it to the veterinarian right away, or refrigerate until you can get to the vet that day. Storing for too long will not give an accurate test result. The veterinarian will need as fresh a sample as possible to test for crystals, bacteria, and so forth.
If the veterinarian diagnoses a health condition they will inform you how to treat it, you can also increase the amount of water your cat drinks (which will help clear up crystals or infections) by keeping the water fresh, and adding some to your cat's canned food. Also look for a cat food that is low in magnesium.
Neuter the Cat
If the cat is an intact male (tom cat) he should be neutered at 8 to 10 months of age. Neutering will reduce his desires to mark his territory. If he is much older this is still somewhat effective although results may not be immediate.
Wash, Wash, and Wash
You must remove all cat urine odor from the places that the cat has urinated in the home. There are many products that help remove the smell of urine however if the area is carpeted you need to be aware that the smell can go deep into the underlay.
Fool with Food, Foil, or Flavors
Putting a bowl of cat food down where the cat has urinated may discourage it from using that location again. Tin foil has also proved effective when placed in an area where the cat would frequently pee.
There are also many products a person can get to deter a cat from going in a certain place, many use oranges, a smell that most cats dislike.
The Litter Box Itself
A rule of thumb is one litter box per cat, and ideally one extra. If you do not have enough litter boxes, add others, selecting different styles than that which you have in case it is the type of litter box that is the problem.
Moving the litter box can sometimes help, but a poorly placed litter box that triggered the problem to begin with (such as having it next to a scary laundry machine) is not always easily forgotten.
Keeping the litter box regularly clean is a good idea.
Use a litter that most cats like best – non-scented, clumping.
If the problem was related to the cat being declawed, try using shredded newspaper in the litter, or simply placing a diaper in the litter box and let the cat use that.
In some cases you can help reinforce correct litter box habits by confining the cat in a smaller room with its food, water, and a litter box, for part of the day, when you are not home, or at night.
Reduce Stress Factors
A cat who is stressed will often urinate in the house, this can be due to the incorrect introduction of a new cat, the arrival of a new baby (in which case the cat may just need more attention), or any other number of issues that their owner perhaps has not considered.
There are stress remedies for cats, the most popular is the Bach Flower Rescue Remedy, available in some pet supply stores, and most human health food stores. Some people have resorted to using a drug, cat prozac, to change their cat's behavior to control problem spraying.