A fantastic question:
“How do I get the sensitize, forward Arab type to stop running off?”
Many Arabs and light muscled horses are of course naturally sensitive and forward. This is a great thing! However, they can be tough to balance. Their necks contract and over bend easily, and they often give in the neck before lifting g the back. This allows them to look “on the bit” without ever lifting or relaxing their backs. If you can imagine carrying a big box of books way in front of your body, you might speed up to keep your balance. Instead, we want to bring this box in closer to the body. To do this, we need to teach the horse to bring the hind legs up under the body. Unfortunately, going through the reins and focusing on the head set first will only further contract the neck and bring them more out of balance, which makes them worry more.
With a horse like this, my first priority is teaching them to find a steady tempo, and to line up straight from nose to tail. Then, I work on getting their front legs to land soft and to extend forward out of their birth area. You’ll find horses like this throw their front legs down quick and hard. Once we have this soft, rhythmic tempo, their hind legs start doing work. You may find your rushy, forward horse is a little sluggish at this point because they are actually using their core and tire easily. I try to maintain empathy for them and not exhaust them. A few mins of a good walk and trot like this is plenty to start.
When the hind legs and back are working together, only then can your half halts be effective. Until then, your reins only stiffen the back and shorten the neck.
You can do all the one rein stops, pulling, making them go on contact that you want. But only when a horse like this feels balanced will they feel secure enough to actually slow down on their own.