If none of the pointers above help, and everything that you try fails, pop your dog in a crate with a dark cover thrown over it. A dog won't bark if it can not see anything to get excited about, and will not be calling for you if it can not see. Leave the radio on for some company and hopefully he will then just go to sleep.
Leave some water in there and a little chew toy or bone whilst you are out, and not for
any longer than a maximum of 4 hours.