My cat has been pooping outside of the box for a while now, and I'm starting to get fed up. He used to urinate outside of the box as well, but that issue was resolved. We've tried many different boxes, different places, different litters, and more. I don't know what to do anymore. He sticks his butt outside on the edge of the box, and the poo rolls out onto the mat instead of into the box. I don't think he's intentionally going outside of the box. We cannot find a box that tapers inwards to make it roll in, and even if we did that isn't a solution, it's just a quick fix. What could be causing this behavior, and what could I do to fix it?