Bama who just turned 14 has started standing to pee recently and the stream ends up going over the sides of the litter box. He's chunky at 17 lbs. He has the extra large size litter box already but he prefers to pee as close to the side as possible. The box sits inside a lid to a plastic tote to act as a sort of mote and I have pee pads all around the outside of the box. I don't think an enclosed box with top entry would work given his age. He used to have a box with sides but he was so cramped and ended up peeing out of the entry way so I got him the extra large box. Maybe a smaller litter box inside inside the XL litter box to move him more to the middle?