I have one per cat plus one. But I will not put one on every level of my house. They're so used to going in the basement that it isn't a problem. I just can't have them in eating areas. I just can't. I know that Specs is occasionally a behavior problem but w/Clomicalm, that's all history now. I just cannot look at litterboxes all over the house, esp. when people come for dinner, which is often. I entertain a lot. As I've said before, this is our house but my rules. And my rule is that they go to the litterboxes in the basement. I realize some of us don't have that option due to space restraints but fortunately, that isn't an issue for me.