The title of this post says it all. I finally got good and consistent canter departs. It all came down to having him working off my seat.
Our ride started with him running through my half-halts. If I didn’t go to my hands, he just kept trucking along. I ended up stopping him and backing him up. We did that a few times before he got the idea. Then we went around the ring with me half-halting him at E, A, B, and C, or wherever I felt him not listening. Then, in one corner I asked for the half-halt, sent him forward and asked for the canter. And he did it. We repeated the sequence in the other direction and got the depart in that direction too!
Now we just need to get our downward transitions. They were atrocious.