It's the Natural for Boxer Breeds. First Train him to Listen you , Improve eye contacts. Never punish him , Just make him away while biting some thing Use The Command "Leave" while doing this . Use command in a Dominate voice , After that Praise him give treats . Repeat this when ever you find him mistake. With in a 2 days he will be come all right . Never punish and use the word "NO".
Don't allow him to play with all the things , give him some toys and make him sure that is belongs him.