This made me laugh so hard.
Me too! Good one, Marecare!
The thing I've found very helpful for slowing down my mare's canter (I think of a canter being a fast, longer strided, version of the lope and the lope being a slower, shorter strided, version of the canter) is just going for long canters.
I take her out on the trail and get to a maybe a mile long stretch of relatively flat, pretty straight, trail and I ask her to canter. I don't let her stop until I ask for it and I usually have her canter the entire way. She's discovered that loping is a much more efficient way of getting that stretch done. At first she'd try to canter fast and, I assume, "get it over with" but by the end she was SO tired. I figure that eventually something clicked in her brain and she realized that if she stopped trying to be so fast, she'd feel better at the end.
It took a month or two of doing that once/twice a week but now, whenever I ask for the lope/canter she automatically starts loping. I can ask for her to canter but her auto "setting" is loping.
I think it also helped cantering be less exciting. Before I only asked her for short stretches of cantering and she loves to canter, so every canter was oh SO exciting, and therefore fast.
Hopefully that all makes sense and it somewhat helpful! :)