I used to stick some of Gunther's toys in the freezer, frozen peanut butter in a kong is great. Keeping him tethered to you to correct unauthorized chewing, and mental stimulation as well as physical which you do a lot of. When Gunther was 6 weeks old I bought some plastic cups and put 3 down with a treat under one of them. They also sell puzzles that you hide treats in, as well as working on tracking. I would designate his favorite toy as his reward during games such as hide and seek, finding the treats, and other games. I have heard of some people carrying bitter apple spray and spraying it into the pups mouth when he snaps at you but I don't know if that works or frustrates them further. Snapping isn't something I've had to deal with.
Hail Gunther 7-2-2013
If at first you don't succeed, destroy all evidence that you ever tried.