I have two boxes and they are kept in the basement and located side by side. My thinking is what you said Jen - what if they both have to go at the same time? Since I have to feed my boys separately now with Trevor's diabetes, I often just stay downstairs until they are finished eating. Andy is fed in a large dog crate and when he is finished I let him out. Trevor is done way before Andy - no surprise there! Anyway, after Trevor eats he goes to Litter Box #1 and pees and then jumps every so gingerly into Litter Box #2 and does the other.