Anyway, I need to fix it, so I went back to square one. I started riding him on the buckle and bumped him up from behind until his neck was reaching as far forward as it could. He's been 100% consistent with the lighter contact the past few days. I am now trying step 2 and taking starting to take some contact back. I am being very careful to follow his motion so as not to block him up front, but he is still taking the option of ducking whenever he gets a chance. I realize I am dealing with an impulsion issue from the back end, but he's a smart boy and has my number on this one. I could really use some help on how to address it. So far I've tried:
Asking for more impulsion. I get the response from behind, but as soon as I take my leg off again, his head and neck go back BTV.
Shoulder-fore and haunches in. Works great...for about 3 strides after we're back on a straight track and then he's back BTV.
Walk/trot transitions. Same result, about 3 strides after we're walking again.
Walk/Canter transitions. These hold the results longer, but only because it gets him so up and goofy he forgets to do his evasive manuever.
He's fine trotting. He'll trot around all day on contact with his nose slightly in front of the vertical. Canter's okay. It's just the walk. He's wicked smart and has my number on this one. I'll try to get video over the weekend. Any help would be greatly appreciated.