Bonus is that the cat can keep his head outside the box whilst doing his business and can't be ambushed by the dog. This may be part of why the cat doesn't like the covered box -- the dog may have interrupted him and scared him. As long as the cat isn't over the weight limit, these things are a dream, and they've limited tracking of litter for us. Also, another added bonus, regular 30 gallon trash bags will make excellent litter liners.