Yeah, I think I know where stunt is going with this. Most turtle keepers will tell you that if the walls of the turtle enclosure are see-through like a screen the turtle will constantly try to crawl out to the area beyond. I, myself, haven't had much trouble with this. They seem to settle down after a while and stop trying to escape. Maybe my luck is unusual? I'd definitely wait to hear from others about this. . . I’m not an expert.
I have the same experience. My pen's walls are hardware cloth, and I have no problems with the turtles trying to "crawl to the outside." I HAVE had problems, however, with solid-walled enclosures I've used in the past.
My take on it is that the turtle gets into a corner and attempts to "burrow into it" because the corner is often a little darker than the rest of the enclosure, and the two walls on each side give a feeling of security, which the turtle tries to enhance with the incessant digging.
Chris