A lot of my last few rides have been working on Archie responding to my seat. Thanks to 100 Whatever, You Suck As A Rider, I've learned that I've been reversing the pressure of my seat bones, oh... my entire riding life. You know, twenty-plus years. Fuck, I'm old.
So it's been a lot of walking, over-dramatizing the pressure of my seat bone, making the answer to my question as easy as possible, praising the fuck out of him when he gets it, and immediately bringing my seat back to neutral. I have a harder time with this madness at trot, because there is such little time with my bum in the saddle. And since we do walk/canter transitions (because I have almost successfully broken the habit of chasing him into the canter), it's been pretty easy for me to do the same walk exercise while setting him up for canter. I derped last night, got frustrated when I couldn't get him to pick up the right lead, which led to him getting pissy and confused. So I stopped, walked for a moment, reassessed where I was sitting, where my upper body was, and bam. No problem.