Halt is beyond us right now

The training test A has one halt, at the end.  The three day test has three halts, spread pretty evenly throughout.  Yesterday, Duke could barely manage the halt at home, but during warm up at John's, he was ok.  I told John, and we started, and Duke was pretty ok, but a few halts in he started to panic.
So the silver lining is John was sitting right there, and worked us through it, but the cloudy part is that we spent our last lesson before Rebecca working on the halt.  (Instead of on the "hard" moves in the test.)
John had us do lots and lots and lots and lots of boring transitions of varying lengths.  One gait difference only - so halt - walk - halt - walk - trot - walk - trot - walk - halt - etc.  NOT trot to halt or walk to canter.
He said to do that in warm up at the show.  Just make it not a big deal.  If Duke is starting to get wound up - afraid of what is about to happen next - just be like "dude, chill, you've got this".
And if he gets wound up in the arena, then blow the move and let him relax.
John also said to give him a bit of leg yield if he's wound up.  Even if it's the middle of the test, move him over.
John also had me give a lot with my hands, at trot and at canter.
He said Duke did better than he expected (since last November, when this happened, it took me a month to teach him to halt again), but still, this blows.  I feel like we're going into an exam for a class I never attended and naked.
By panic, I mean he spun, stepped sideways, smashed my leg into the wall, stuck his head straight up in the air, and twisted around.
What's the worst that happens?  we get eliminated in dressage again (and so I'm eliminated 2 out of 3 times at Rebecca). What's better than that?  We finish the show.  Jesus, the bar is low.
But a year ago, I could hardly steer him around a show jumping course and he was so unbalanced at the canter he was hard to ride going to the right.  So this is progress, Martha, try to remember that.