You working with him one day a week is a waste of time. Sorry. If he gets to practice the behavior everyday with no consequences, then you will never fix the issue.
Keep him inside when you are at work. Don't allow him to behave this way.
When you are home, have him on a leash and collar and start redirecting and training him BEFORE the mailman arrives. Once he goes into bark mode, it's too late.
Sent from Petguide.com Free App