You could maybe try leaving food in a kong toy or a biscuit ball to keep him entertained during the day while you away. It might help to relieve any boredom he feels. My two love getting their kongs full of food (I swear they look forward to me leaving so they can get them!). I usually put in a piece of something that's hard to get out so that once they have most of it out, there is a piece that they need to work at for a while to try to get out (a large piece of freeze dried liver usually does the trick).