How can I discourage my cats from peeing on the furniture?

Try cleaning the litter boxes every day. How many cats and how many boxes? Should have one box for every cat. How often do you change the litter and scrub the boxes out? Cats can be very sensitive to odors. Perhaps it is the litter itself they don't like. Many cats don't like scented litter. They have VERY sensitive noses and strong smells can be too much for them to handle.

But in the meantime clean with Nature's Miracle Spray. It has an enzyme in it to get rid of any urine odor.

Hopefully this isn't a sign that the cat is ill. Could be time for a trip to the vet if none of the above helps.

They have sprays that you can use to discourage them. I use pledge ORANGE furniture polish on my counters christmas tree, knik knack shelves and this keeps mine off of what ever I spray. Orange oil works great but it will ruin furniture

In my years of cat guardianship i found the usual causes are 1) dirty litter box, 2) urinary infection, 3) behavioral issue (sees/smells other animal in or outside and pees to defend his turf.) Are pee spots near windows where your cat might get intimidated from outside animals?

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if they haven't been spayed or neutered yet then that will definitely help