I did see a few days ago Bob got into the low one with the cut-down sides, but then he kept falling off over one side or another and tipping it. He really needs the high sides all around except for the opening.

I put it up against the corner walls so there are at least two sides to lean against now. But now that I know what to look for, I'm going to get a couple more of those Rubbermaid boxes.

I figure the litter kicked out through the low openings is just something to deal with for these guys. I have litter mats in front of the openings so most of it lands on them, and then I just pour the litter from the mat back into the box.