Have you thought about some interactive toys for your dogs? First, is the Buster Food Cube. It comes in two sizes. You drop dry kibble or treats in the hole and they get lost in the hard plastic cube. The dogs very quickly learn to roll it around with their noses and paws. Occassionally one of those treats falls out and rewards the dogs for their efforts. Dogs love it! I had 3 of them, one for each dog and it gave them something to do while I was gone.
There is also a similar toy that's a ball and serves the same purpose. Kongs are great toys as well. Fill it with treats and plug the hole with a large milk bone type of treat. The dogs have to get that tight bone out before they can get the treats.
I would also check to see what's going on when you leave. Once I drove down the street, walked back and peeked over the fence and in the windows to see if there was any weird behavior going on, like one dog being aggressive to the other. It gave me a lot of insight to the problem I was having. It sounds like your dog might be having an anxiety problem. Often these interactive toys will help solve the problem.
