Odd that yours haven't picked a corner yet - I've yet to meet a leo that didn't have a consistent bathroom spot right away. In fact, the one I currently have has stayed the same through a few moves, even though the north/south/east/west orientation of her cage has changed. The poop is always in the back right corner of the tank, no exceptions. She even stayed the same when we moved her from a 10 gallon to a 20 long a few years back.