Quick update - we've made real progress this week, although it doesn't feel like it when we first arrive at the park and he is pulling and barking like fury! But he is settling into nice walking much more quickly. He's still orientated by get a treat, so walks gazing up at my hand. I'm stretching the length of time / number of steps before the treat comes, and he is also occasionally just walking by my side, looking around.
He still pulls more for my OH, so I got him to walk Henry most of the time this morning. As ever, the OH needs more training than the dog! He kept allowing the lead to go tight because 'oh, he's only pulling a bit, it's better than it used to be'. I insisted on zero tolerance on any tightness in the lead which is boring, but being inconsistent is what got us in this pickle in the first place.
The other thing I've noticed is that Henry is getting a little less reactive to squirrels, which has been a big issue for us and his recall. He stops and stares, and whimpers a bit, and still pulls towards them, but not to the point where he's on his hind legs. And I can get his attention back to me much more quickly now. There were a few times today where I noticed him get distracted but then very quickly turn his attention back to me without being promoted. Hopefully this is will help in re-training his recall, which I'm starting in earnest next week.