I tried to follow what you all described, and I read thru the thread Kayty posted. I think I understand what it should be like, but right now I'm kind of trial and error with actually doing it with my pony.
The way I figured out worked the best was just like 'checking' a little bit with the reins and just kind of bracing/shifting my seat a little. I really felt him load up, like a loaded spring kind of. (I can really feel it bareback, because his back muscles change.)
I found that it only really seemed 'work' to me at a canter/lope. He just thought he had to slow down at a walk and trot.
I really felt a good half halt while I was taking him from a canter to a gallop when I was breezing him around the pasture bareback!
It really is seeming like a good thing to know! I hope it helps him get his back end working harder than it is (he's a bit heavy on the forehand)
We're working on it! Thanks for letting me know!