We had a cat who liked to adopt a wide stance that always ended up putting her tail off the edge, so we got her a larger litterbox and that problem ended. Another time, we had an old cat that started peeing outside the litterbox. We had her checked for medical issues (UTI, diabetes, etc) and none of the usual suspects. But she did have arthritis. So we got a slightly larger box with a really wide but really low front lip so she could get in and out easier. The problem stopped immediately.