Spider and I are both crooked. And we're both crooked in the same direction, unfortunately. If we were crooked in opposite directions we could potentially even each other out. But, no... we both fall in to the left.
Now, it could be a sort of "chicken or egg" dilemma. Is Spider crooked because I'm crooked and I'm the only one who rides him? Or was Spider always crooked and he made me crooked by throwing me left while I was weak after my injury? Or are we both just crooked in our own special, completely uncomplimentary ways? Doesn't matter. It needs to be fixed.
See, what happens with a crooked horse is that you're going along quite nicely (or so you think), until it comes time to turn. Then, you're suddenly careening out of control and into the bushes on the side of the arena, or getting quicker and quicker until your horse is completely on the forehand and you're leaning into the turn like a motocross rider. Not really ideal.
My first fix is always to check myself: Am I leaning left? Yes? Then I look over my right shoulder until my hips and shoulders straighten, breathe in, and turn my head back to center. The human head weighs quite a bit. Simply turning it forces our spine to realign itself and the hips and shoulders follow along.
Next I ask myself, "Are we still crooked?" Yes? Time to re-balance Spider.
First we do a couple quick transitions up and down. And by quick, I mean just a few steps in each gait. This gets his balance shifted back onto his haunches. Then, I take a few steps of shoulder in to the right, followed by a few steps of haunches in to the left, then circle left. The circle left is the "check" to see if he's really supple or not. If he falls in, we repeat the exercise.
When Spider is crooked, he falls in to his left shoulder, and loses the contact with my right (outside) rein and leg. The shoulder in right re-establishes that contact and lifts his inside (left) shoulder. Also, when he's crooked, his haunches drift out to the right and his body loses it's bend to the left. Once I have the outside aids back, the haunches in left brings his hind end back around and re-establishes the left bend.
Obviously, a haunches in is not the way we want to go around all the time (certainly not in a show!). That would be wrong, just as wrong as having the haunches out. The horse should be straight. But, because Spider is crooked, we need to exaggerate the movement to strengthen him and build flexibility. This is training, not showing. You exaggerate the training, so that you can make it look easy at the shows. The ugly riding stays home!
As an added bonus, both shoulder in right and haunches in left require me to get off my left seat bone (remember I lean left), straighten up and balance myself. It's an exercise that works both horse and rider.