Cats are wonderful, empathetic companions that delight us with their antics. They can also be horrible nightmare beasts that throw up right where you step out of bed, and crap in your shoes. The most common reason cats are surrendered to shelters is inappropriate urination. (Otherwise known as peeing where they shouldn't.)
Find out what the problem is.
There are two reasons cats pee outside the box. It is either a medical or a behavioral issue.
Its best to go to your vet first, to rule out any medical issues. Pain while urinating can cause cats to seek out a place to pee that doesn't hurt. Which leads to random spots all over your house.
Collect a sterile urine sample from your cat. Your vet can supply sterile litter that looks like ice cream sprinkles for your cat to pee in. This may require them being locked in the bathroom by themselves for a bit. Your veterinarian will analyze the sample for blood, white blood cells, and crystals. This will tell them if your cat has a urinary tract infection, or something more serious. A clean urine sample means that the problem is not medical, but behavioral. Which is both a good and bad thing. Hooray, your cat is healthy. One the other hand, why are they doing this to you?
Cats can't tell you that they are really upset that you've changed things in their life with words, so they do it with their toilet habits.
New people or pets in a cat's life can trigger a stress response, as can moving, a different work schedule, etc.
Identify what has changed.
Look in the mirror. Repeat these words. "This is probably my fault."
That's the hardest part.
That boyfriend you have that your friends aren't crazy about? Since he's been spending the night, your cat has been peeing on his pants, and your bed. She doesn't like him either.
That adorable puppy you adopted? The one that chases the cat,and whines when no one is paying attention to him? What a racket! This is a huge disruption to what used to be a peaceful daily routine. Time to pee in every corner there is.
Sometimes it can be an obvious thing, other times, its a bit more subtle.
With multiple cats, there should be multiple litter boxes. The general rule is one box per cat, plus one. Some cats share boxes without any issues, others are territorial about where they go. Sometimes, especially in houses with a large age range between cats, a younger or more dominant cat might ambush another cat going in or out of the litter box. This makes that cat feel unsafe about using the box, so they go somewhere they can keep an eye out for trouble.
So what can you do?
With the litter boxes, keeping them clean can cut down on a lot of problems. Scooping every day can eliminate problems that stem from having a very fastidious cat. An unscented litter is best.
Trying an open box and a hooded box can help determine how they're feeling about the litter boxes in general. Some cats like to see what's going on while they go, others like to feel more private. One of my forever cats is a high peeing cat. His stance guarantees that without a hooded box, he pees on the wall. He's not being a jerk, he just likes taking up a lot of space.
If an area smells like a litter box, cats will use it accordingly. Even if you address the life change that stressed them out in the first place, if the places they've gone outside the box isn't well cleaned, they may return to it. Jerks. Nature's Miracle makes an enzyme based cleaner, or you can use baking soda and white vinegar to scrub the spots.
Get up as much of the urine as you can with paper towels or a sponge.
Mix 50% white vinegar and 50% water together in a container. Let that soak a bit, and then blot it up. Dump some baking soda on the spot. Don't be stingy! If the baking soda turns yellow, vacuum/sweep it up, and apply a new layer. Mix a quarter cup of hydrogen peroxide with a teaspoon of dish soap. Scrub that in ( I like using a toothbrush) and let set for 15 minutes. Blot up the remaining liquid, and add another layer of baking soda. When the baking soda has dried completely, vacuum/weep up, and your house should be odor free!
If you have the space, try feeding them small amounts of wet food on a dish where they went outside the box. You don't sh*t where you eat!
If a new pet is causing the stress, add more vertical space or hiding places for the original cat to utilize. Cats should be introduced slowly...if they have terrible first interactions, they tend to hold grudges. I'm a huge fan of baby gates.
Have the new cat be in their own room, with a door that is kept shut. The cats can interact under the door for a few days. Then, you can put a baby gate up in the doorway, with a blanket blocking the top bits. ($4 tension rod comes in handy here.) This creates a visual barrier that inhibits the cats from leaping over the gate and getting into a fight. Using wet food or treats on either side of the baby gate allows the cats to associate each other with something positive. Make sure that they can see each other, but aren't so close that they feel possessive of their resources. Hissing comes from fear, growling comes from anger. If you have a lot of vocalizations, take it slow! Its far better to have a drawn out introduction than live in a war zone. Happy cats will play with each other, and socially groom. Unhappy cats will spat with each other, and mark up your house.
With dogs, make sure that introductions are low energy and reward the canine appropriately for good behavior. Putting the cat in a carrier so that they can see the dog without the dog being able to get to them often works, especially if you have the dog stay laying down, and treat good low energy interest. With effort and attention, everyone can get along!
Another layer of support is Feliway, a synthesized pheromone that mimics what feline mama's exude. This ~usually~ has a calming effect. I use it when I have new arrivals that have been dumped, or come from traumatic situations. It can be mildly calming, or eliminate issues altogether. This completely depends on your cat and the environment. It has no smell that you can detect, and can only help. I recommend the plug in over the spray. It emits pheromones continuously, and can be used either in the room where the trouble is happening, or in the room where the cat spends the most time. Rescue Remedy also makes flower essences for pets that you can rub on their ears to soothe their rumpled emotions.
Cats that are fed a high quality wet food are far less prone to urinary tract issues than cats that subsist only on dry food. Even doing one meal a day of only wet food can make a drastic difference in lower urinary tract health.
So. Your plan of attack with a "problem" kitty.
Ascertain if it is health, or lifestyle related.
If it is health, up the water intake, and administer any medications prescribed by your vet.
If it is a behavioral issue, look at what has changed recently in you and your cat's life.
Make the house feel as safe as possible.
Stay on top of the trouble spots, so that inappropriate elimination doesn't become a habit.
And above all, don't get discouraged. You can do this.
The Captain of Browncoat Cat is a self proclaimed crazy cat lady. Of course, we're all mad here...