I’ve been down a few trails (especially in Vermont) that were steep enough to give me pause. In fact, the first summer I had Freedom we went down a pretty technical hill where at one point, he literally just sat down because he wasn’t sure what to do.
These hills, however, make the hills I’ve tackled look like ant hills. The photos are taken from Cavalry training.
Reading a bit more about these kinds of steep down hills it appears that your best bet is to lean forward, rather than back as you help your horse’s braking abilities by putting more weight on their forehands. Not sure I’m brave enough to try that.