Have you ever been around a blind horse?

Did you have trouble stopping either of them when they were either nervous or eager? Iris is a real sweetheart, but under either condition above she just wants to keep on walking. Never runs/bolts (afraid to run into things, of course). The feeling I get from her is that when she's nervous, she just "needs to keep moving her feet". We then land up walking her in a circle. Probably this would be like trying to bolt if she were sighted. Oh, and she's 18H, so it is sort of a "big deal" ;-) pun intended

With her size, you definitely don't want her getting on top of you. The walking in circles is fine. If you're wanting an alternative to that, I'd suggest a a sharp jerk on the lead shank and a loud angry tone in your voice when you say "stop it!" or "Quit" or whatever words you choose. Tone of voice works quite well in my experience on correcting the horses most of the time. They don't like an angry tone! If that still doesn't produce the results you're wanting, add a chain over her nose or under the jaw. A chain under the jaw is kinder than over the nose, but when you jerk it, it can make them want to move forward away from the pressure. A chain over the nose will make them want to step back. Do not get too rough with a chain, you can hurt their nose. It doesn't take much pressure to get their attention. Hope this helps?