It's really the same old story; the horse is as pushy as you 'll let her be. So, if you don't expect and require her to stop when you say "stop", then you wont' get that. HOrses rise to the lowest level of our expectations. So, if you accept a slow, sloppy stop, then you will get that.
So, if you stop, (and be sure that you have given the hrose a bit of prewarning with your body by shifting your upper body backward, as if you are leaning backward a bit, jsut before you stop your feet) and the hrose keeps going, you have to reprimand that .
I start with jerking backward on the line, and if the hrose doesn't move backward, I use the twirling end of the lead rope, just as the other person said, our in front of the horse 's nose. So, I am backing up, jerking backward on the lead line, (just under the horse's jaw) and as aI back up, the twirling leadline gets so close to the horse's nose, that if they don't move, they end up getting bopped on their tender nose. That usually makes a pretty good impression .
After I do that enough, the realize that once they pass my shoulder, they will be brought back behind me again, so all I have to do from then on is raise my leading hand a bit, maybe give a little shake of the line to remind them to get back in "their" place.
But, if you dont' keep reinforcing this , the horse will forget it . So, if your expectation goes down, so does the horse's compliance.