I just use a long, heavy lead rope, weight is the key.
I clip one end to the surcingle on one side, and use about 6 braiding rubber bands to attach the end of the lead on the other side. The lead rope goes around the horse’s hind legs, laying about 6-12" above their hocks (depending on how they move). As the horse moves, the weight of the rope taps their hocks with each stride, reminding them they have hocks back there, and encouraging to step under. Its remarkable how effective it is. So much so, 10 minutes is max for usage, else they can get sore.
If things get western, and a hock catches the lead rope, the rubber bands snap easily and the lead falls safely away.
Do however, be sure your horse is ok with a lead dragging to the side of them. If they’re not, it can be surprising, especially on the heels of some antics.
I only do this longing, not riding.