Dog Chewing On Wood

Hello all!

I have a 2 year old Bernese Mountain Dog and never had an issue since day one when he was a puppy. We decided to get him a friend, apparently this was a mistake, kind-of. We got an Anatolian Shepard/Great Pyrenees Mix puppy. He is about 6 months old now. Recently, he has started to chew wood. It appears he only does this when we're not home. I have read about bordom and teething. I was just looking for any other suggestions. He is crated at night since we can't fully trust him alone yet. I know some may suggest to crate him during the day when we're not there, this is a problem for us. There are three days that no one is home for a significant amount of time, about 8 hours or more. But, we have a very large fenced in area for the dogs with a doggie door into our enclosed porch that has an air conditioner and a bed and large bowl of water. They have a great setup for the two of them while we're gone. There is no one nearby to let him out often if I crate him, also, I don't think it is fair with the setup we have to not let him be out there. I've used the bitter spray, that seems to work for a bit but he finds another door frame to chew. We have tried the hot sauce, that doesn't seem to work at all. I've taped all the door frames with duct tape last night, we're waiting to see how that works. I've also tried getting a toy that they have to work at to get the treats out of, and only give it to him when we're leaving, not when we're home, doesn't seem to do the trick. We're leaving many toys out for him. We're going to try and really fill a bone with peanut butter, but for us to be gone for that amount of time, I just think he gets bored. He has all his adult teeth in but I know they can teeth for up to 8 months or so.

Any suggestions would be greatly appreciated. Do most grow out of this stage??