So, lesson went really well!! I really like her teaching and I am sad that this was kind of a one time thing, but we got a lot figured out and I have something concrete to work on now.
First thing she did after I explained what I've been working on, was check Nav from behind and right away she noticed that his left hindquarter is less developed than right. Our hypothesis is that since he was off on the right front with white line, his left hind became weak too (since horses work in diagonals, and he was likely favoring those two and putting most weight on front left/back right). He hasn't been tracking up with the left hind and his left hip was a bit sticky. She suggested a chiropractor who could take a look at him, so I'm considering that. Really though, (and these were her words too) it seems to be an issue of muscle development. Once he gets back to working the left hind that muscle will develop and he'll become straighter.
Apparently also it's not that he's not bending to the left, it's that he's not straight. She described it as if for him "straight" is more like a normal horse's shoulder in left. And that's what feels normal to me, so it will take some time to get used to a true straight. Once he strengthens that left hind and becomes straighter the bending should work itself out. He is very supple in the poll and shoulders too, in spite of how broad he is.
So now that we figured out what the problem is, she got to work giving me a bunch of exercises to use.
The first thing she had me doing was a haunches in to the left. This is hard work for him since he hasn't been using that hind, and he wanted to fall out onto his shoulder. She had me going just a couple steps at a time and then letting him rest. The other exercise was a shoulder in to the right. Again, pushing the left hind out and making him put more weight onto it and use it more.
Another exercise we did with cones in a square, though later she told me to do it with a triangle for more of a turn. I started by walking along one side of the square circle. When we got to a cone, did a turn on the forehand (to move the hinds and supple it) and then continue. Eventually we did this at the trot as well. Then change direction and do it again, but with a turn on the haunches instead, to keep him thinking. I'll insert a clip of that here. No music this time, so you can hear my instructor's commentary, though I don't think she said too much. We have a little bit of right canter in it, and while it's not bad, I know it will be better when he is stronger and able to push off with the left hind better.
The other exercise we did was called the Snowman. It was a twenty meter circle and at the end of it, change direction and do a ten meter circle. The goal was to keep him from falling onto his shoulder, and also pushing the left hind out. That was the main goal of all of the exercises, just getting the left hind to work.
By the end he was tracking up and over with his left hind and was much more loose in the back!
One other thing we talked about was how smart Nav is. He begins to anticipate so she showed me ways to change up those exercises. When he begins to rush instead of move away from my leg I need to either half halt and slow him, or come down a gait. And when he gets grabby and heavy on my hands I need to ignore it, keep my hands light and forward so he has nothing to bear down on, and get him working. He knows that getting heavy is easy for him and that if he fights me there then I'll ignore his hind end - which is exactly what I need to be focusing on!
I'm so thankful I was able to have this lesson. While I won't be able to do any more with her, she did mention to me some clinics coming up and said I should come and audit since that's free (which is my price range, haha). So I'm looking into going to one in a couple weeks.