OH Buddy - this is a terrible dilemma you're in. I've dealt with pet odor every since I've had a multiple cat household. However, thankfully all my babies are using the 2 boxes I provide for them. I had a big mess when I had my kittens last Feb. and ended up replacing the carpet in the bedroom where the kittens were born. I've replaced the carpet in the "cat room" with a type of burber indoor/outdoor type carpet and that has been swell - it cleans up really good. All and all I really think you have turf wars going on among your feline family. Hate to say this, but if you want them all to be indoors you gonna have to put up with the smell. Just keep the boxes as clean as you can - clean and deodorize the problem areas and maybe burn a lot of scented candles - thats what I do - just last night a cleaned the cat room and burned a cinammon scented candle in there - it helps a lot. Good Luck Buddy!!!