my stinkpot does the same thing. I use a piece of driftwood that leans against a half flower pot, with river rock along the bottom of it. He likes to climb to the top of the wood and get close to the light and sleep for hours, and also wedge himself between the wood and the side of the tank, shoving the rocks out of the way. So I pile them back up every few days or so. He also likes to push behind the filter. I wonder if maybe they like to feel the pressure on their shells. Maybe it makes them feel secure.