I can't really tell from your avatar, but is the half-log the only hide in the tank? If so, he may not feel secure in it. They are open on both sides and is probably too big for him to feel comfortable. Try something like this...http://www.reptilebasics.com/small-hide-box.html

One on the warm side and one on the cool side of the tank. They don't look pretty, but BP's LOVE them.