Please respond to this question
My cat keeps peeing on the bottom of our staircase. I think I've figured out what started it: we brought home another cat, after one of our cats ran away, and he started peeing all over.
He occasionally pees in the basement whenever the basement door is open.
We've tried having two litter boxes, changing the litter, having only one litter box, changing his food, and we even got rid of our other cat and started over again!
He doesn't have any health issues, he's strictly indoors (Completely by his choice. He hates the outdoors.), the only pet in the house, age 13 in SHY (Standard Human Years), gets attention anytime somebody's home, a Russian Blue breed.
I don't know what to do!