LOL...
I think I didn't communicate my point right...
find whatever level he will not react to, and then practive UNDER that level and reward that until hes comfortable, then up the ante...
if you have to go out the door to leave...go to the door and DON'T leave...as many times as you have too before opening the door and not leaving....then stepping outside, then right back in...etc etc etc...
Dogs are keying in on the cues that lead up to the leaving, not just the actual leaving...they may start stressing when you grab your keys, your jacket, etc... so you must make those things no longer mean that you are leaving...OR you must countercondition him with rewards to not be stressed by those things.