I too had the same problem so I set mine up with a free range inside. I keep my chams outside most of the summer weather permiting. I have him in a huge 3x3x6 foot enclosure with wide pvc screening. He still does what yours does but not as bad as it was. I use neosporin on his mouth. He doesnt have any color there anymore but the neo really helps. I also have his enclosure planted with one huge hanging pothos, 2 giant scheffleras, and tons of sticks and biovines but he still persists.
Dodolah is definatly correct on the idea of him seeing something he wants or somewhere else he would rather be. Make sure there isnt a female for him to see or they will go nuts. Even after mine sees the fem for a second he seems to be pacing trying to find a way out even more. Any big full trees around will definatly make them want to be WAY up there where they feel safer than in an enclosure. I really dont have a solution besides making him a HUGE outside cage with tons of plants to make him feel safe. Also just put the neo on him whenever you see it getting bad. Sorry I cant help much but I feel also that he probably just wants to be in the biggest, tallest, fullest, safest, TERRITORY he can.