Worked on using my inside leg to help him stay balanced in the canter around turns, especially to the left where he struggles to stay balanced. I'm sure this is in large part to his left hock weakness.
Then turning, turning, turning! Turning precisely and from behind. I did lots of sitting the trot while working on turns.
We are getting longer and longer moments of natural collection without ever forcing collection. The turns and asking him to move with energy makes it easier for him to drop his nose without me asking. When he does, I take up the slack and maintain the connection.
We did lots of canter work and asking him to maintain the canter through the turn while staying balanced. Right now, I'm micro-managing in the canter. As he gains fitness and understanding, I expect that to change. The trot is also getting much more rhythmic.
I tend to lose contact when I change my leg position. I need to work on maintaining contact regardless - steadier hands.