The real solution is to crate the dog. I don't think I have ever heard of a dog that was crated from 7 weeks that didn't accept it. I would start with a 36'' plastic crate. Should be about the right size for him. A dog that has not been crated since it was little, may take some work. Start out just putting its toys and treats in the crate. Praise it for going in. Feed it in the crate.
You may want to put it in a corner and put something heavy on the other side of it to keep it in place.
Do not try to leave him more than 4-5 hours at a time. That could be much of the problem. If you can't give him a break, find a neighbor or professional dog walker to give him a mid day break. Finding a doggy day care could help too. Some medication from the vet for a while might be a good idea too.
The key to most behavior problems is approaching things using the dog's natural instincts. Dogs see all the people and dogs in the household as a pack with each having their own rank in the pack and a top dog. Life is much easier if the 2 legged pack members outrank the 4 legged ones. You can learn to play the role of top dog by reading some books or going to a good obedience class. A good obedience class or book is about you being top dog, not about rewarding standard commands with a treat. Start at
Raising Your Dog with the Monks of New Skete For more on being top dog, see
Establishing and Keeping Alpha Position, Letting your dog know you are the boss