Frozen Kong? Sort of Dog Chewing 101 and you may have already tried it, but it doesn't hurt to have a couple lying around in the yard. Plus, it's completely safe to leave them with unsupervised, provided you don't stick something like a cooked chicken bone in it

I was also thinking about just using chicken fencing to blockade the wood. If nothing else, you could lay it over the parts that he likes to chew. That would make it more difficult (but not impossible) for him to chew the wood itself. What I'm thinking is: if you give him the option of a frozen Kong vs. wood with chicken wire over it, I'd be willing to bet that he'd choose the Kong over the wood. But who knows! Puppies are a different kind!