Chances are it's because you have left him alone for too long. He's either frustrated or bored out of his mind... or a combination of both. Is he allowed potty breaks every few hours or is he expected to 'hold it' for hours and hours and hours .. like some people expect from their pets.
You need to get your dog food puzzel toys round $20-$30 each & kongs. $10 upwards. Fill each one with different treats & also leave a bone or two. A few stuffed toys with no chokeable parts. ( like a babies first teddy.) This allows them a variety of entertainment while your gone. Maje sure plenty of fresh water also. If necessary confine him to one room, say the laundry or back veranda. Goodluck. Failing all this then maybe you need professional training