Unfortunatly my male cat (altered) is doing the same thing, he is now confined to the basement which has all tile floor with his litter box down there for him. The kids spend a good deal of time down there as that is where the game systems are, and I do quite a bit of laundry per day so I am always up and down the stairs by him, so Spencer is still getting plenty of attention and loving. I discovered I need to keep his litter box CLEAN. I have to check it multiple times per day and right after he does his thing, I have to clean it or the next time he will use the floor. It's driving me nuts but it's the only option I have