What I do with my dogs... (Both are chewers, but me shepherd mix is thick skulled so he gets crate time when we're not here)
...is exercise them until they don't have the energy to get into everything. Sounds like a lot, but a two mile walk/run will do wonders. My pit's getting old, and can't make a long run anymore, So with her, a couple laps around the block works.
When I had a pit/lab mix puppy, I'd flick him on the nose and tell him no when he'd try to get into something. I found out that with labs and lab mixes, positive reinforcement works better than any other training I'd come across.
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