One of our cats is rather elderly and refuses to go outside to pee at night now the weather has turned cold. Fair enough, we put out the litter tray. The problem is that an uncovered tray is a source of toddler delight (we have an 18 month old) and the cat won't use a covered one. It's also a fairly small and open house, so roping off a room for the cat is not easy. WWYD?