Three poles set up in a fan pattern in the corner, with the fourth about two or three strides away. We did it at the walk, starting with just a big warmup around the ring, getting him a little bit loose and swingy and a bit softer and more bent.
Then we did the two poles on the outside line, which were set up so I could avoid the corner fan, and got him to start lifting his back and really stepping over the poles.
Then we incorporated the fan into it, staying in the middle but still going all the way around the ring. This proved trickier, since a) I hadn't gotten the striding quite right and b) Tris still wasn't really with me yet.
I took a break from this to ask him to canter a bit - not really a lot, or to school it, just to get a bit more jump in his step and to get him thinking a little more forward.
He was reluctant to canter, through, I'm sure some combination of stiffness and my lack of really solid seat with the bareback pad contributed to that. Once he did, he moved much better.
Then we moved to a smaller circle and worked over just the fan of the poles. The nice thing about having them out like that was that I could guide the exercise more specifically. We worked on the inside of the poles, requiring a much tighter stride, and then on the 15m circle we spiraled out and went on the outside of the poles, which meant a bigger stride.
I was really pleased with how the exercise worked out, but not necessarily with how I rode. I just wasn't quite present like I needed to be to handle Tristan's stiffness and unwillingness that day.