Maisie gave me a job on this ride. She would walk calmly and with a regular pace, and softly - no rushing - if I didn't use my reins to ask her to slow down or stop. So since I couldn't use my hands, I had to give very slight half-halts with my seat, to ask her to slow or stop. We marched along - I held the reins in both hands with a very light contact. She was walking along very well with a nice swing. Any time she started to think about picking up the pace, I asked her to slow with a very brief half-halt with my seat, keeping my reins and contact just the same. I would describe this as really not using an aid, but rather just taking advantage of the horse's natural tendency to slow when the motion is even slightly blocked. In effect, instead of letting my body move freely with the horse as she walked along, when I wanted to slow I would very slightly "resist" the naturally free movement of my body on top of the horse. This was enough to slightly block her motion, causing her to slow just slightly. I doubt that anyone watching would have been able to see anything at all, since I tried to do this as she was thinking about speeding up, rather than after she did, and I wasn't really moving my body at all to ask her to slow - just not moving my body as freely.
It worked like a charm - Maisie was very pleased with my progress! Now she says I need to refine it so its even more subtle and not so "loud" - I didn't think it was that big but she says I can make it much softer and she will still hear what I am saying.