Gee he is a year old. Maybe if he could somehow confine him. There are large crates for big dogs. He shouldnt be left to run free when alone maybe.
Is there an enclosed yard that is safe to put him in that he cant get out of or anyone get into.Maybe he gets nervous in the house by himself.
Maybe this is why he was in the shelter. He might have had this problem with his last owners.
I know you will get much better advice soon anyway. I am no dog expert for sure. I am just guessing here.