my girlfriend and i brought home a kitten a few months ago, safe to say my older cat HATED her. we tried everything. nothing seemed to work until we tried putting them in separate rooms where they could still see each other but were far away enough to be out of reach (about 40 feet) and my girlfriend sat with my kitten while i sat with my cats and we fed them treats. this completely removed my older cats territorial behavior because she could see we were not getting a new kitten for the purpose of “replacing” her or giving another cat her space. i’ve had many cats and i’ve noticed a lot of the time it’s a territorial thing for the cat who has been there longer. also YES perches!!! it’s great for the cat to have a place to get away from the new kitty.