I believe his problem is a mix of anticipation and concern. The closed bridle is new to him, I've been driving him around in increasingly unfamiliar areas, and he absolutely anticipates moving forward again after stopping.
This is a problem that I could solve under saddle by making him want to stand when I ask, but doing that while ground driving sounds like a lot of running. I hate running... I'll have to go back to the round pen for the halt if I'm to go that route, but he always stops great for me 100% of the time in the round pen! I think I can stop the anticipation thing without getting any cardio in, or at least make that anticipation work to my advantage.
I do get your point with the catholic school analogy, but personally I'd rather not be taught mathematics at all!
Do you think that maybe backing up every time I halt him so he learns to anticipate that could help? Kind of like what reining trainers do.
I've actually tried telling him to walk off before he starts to do it himself, and that made my problem worse... He'd just anticipate the cue to move forward even sooner.
I have no intention of hitching him until his halt is perfect. I've seen what can happen with ill mannered driving horses.
But I do make it a point to spend time with my horse and chill before and after every work session. He will stand perfectly for me until he's in harness and in a place where he can really move out. He's a very curious boy and I can tell when his mind wanders from the task at hand.
Under saddle, it's the same deal. He's perfect in the round pen, but he gets a glimpse of that big open arena and he just wants to go. His canter to trot transitions are great, and so are his trot to walk. He obeys those cues without question, it's the standing still thing that he objects to so much.