do you kennel him when gone or is he free to roam? sounds like he needs some separation training ... he needs to understand that he is ok when you leave and that you will come back. I would start by doing little amounts of time while you are home to monitor him put him in his crate or the room you leave him in when your away from home and when he barks correct him then leave the room again and wait outside the door if he barks go back in and correct him again (using a "atat" sound or tsssst or whichever sound you choose) it will take time, patience and consistency .... doing this over and over until he understands that the barking is not ok ... he will catch on and will eventually settle down while you are away. make sure you praise him A LOT when he is quiet in the room/crate and allow him to come back out and visit, he gets the reward of your company when he is quiet. good luck and hope that helps a little.