Litter Box Training
If your cat urinates outside of the litter box, you likely have gotten upset at them and thought that punishment will correct the cat's behavior. You should avoid shoving the cat's nose in the area he urinated at or smacking him because this only scares the cat and he still won't recognize the behavior you're asking him to do. The first step to correcting litter box non-use is looking at the likely reason your cat goes to the bathroom somewhere else.
Why Your Cat will not use the Litter Box
The most important consideration you should make is that your pet could have a urinary tract infection. Check with your veterinarian to make sure your cat is healthy.
A cat could react badly to introducing a new animal to the household. Multiple cats may scare each other off from the box, or one could dislike sharing its space with the other. Try getting more litter boxes and see if your cats make their own bathroom choice.
Did you get any new furniture or place rugs recently? If you see an affinity for a type of surface your cat prefers to go on, the best thing you can do is remove it until he readjusts to using the litter box.
If you notice your cat goes potty while you're out of the house, you should confine the cat to a room with food, water, and the litter box when you leave. Place the litter box far from the food and water and make sure the box is clean.
Clean up soiled areas of your home with a non-ammonia based cleaner, otherwise your cat will go in those places again. You need to set a schedule to feed your cat and to play with him. Cats usually need to release their waste after eating, playing, or sleeping for an extended period. Watch him after playtime and see where he goes to the bathroom. If he went in an inappropriate place, pick him up and take him to the litter box. Do not be angry with him, and praise him when he's ready to leave the box. This positively reinforces the behavior you want from your cat. Within a few days, your cat may go straight to the litter box when it's time to go-and you should give him love and praise!
Litter Box Type
A final, but important consideration if your cat doesn't respond to a regular schedule is that he may not like the box itself. If you have an enclosed box, try an Open-Top Litter Box. You could move the box somewhere the cat would see more convenient, or have a box on each floor of your home. Cats in general prefer low-depth clumping litter. Try litter with crystals or different amounts to see if that makes him happy and comfortable.
Do Not Give Up
You can go through a lot of trial and error before you satisfy your cat and re-train him to properly use the litter box, but persistence is the only way you can change a behavior that has already set in. Keep your goal in mind, even when he frustrates you, because you love your cat and you want a happy, healthy companion for years to come.