After my gf and her cats moved in with me and my cat, my cat has taken to spraying on things. Mostly it seems like he sprays on one of the litterboxes instead of in it, but I've also found piss on a cabinet, on some walls, and on a desk

We're moving into a house in a few months, and I don't want the house ruined, so how do I get him to stop spraying on things? I don't want to banish him to living in the garage