I agree with Gemy- crating him when unsupervised. It was the ONLY way we could trust our lab in the house. He would chew EVERYTHING (and still does when we hop in the shower and he wants some fun-- bathroom garbage, books, CDs, glasses, coffee grounds, bottle of booze, containers with anything in them...etc... the list is a mile long haha) but when we are home and with him he is very well behaved. He gets bored and misses us, so he eats our stuff... makes sense??
hahahaha
Best of luck with the Boxer. My BF used to have a Boxer and he swears they are one of the smartest and best dogs in world. :-)