As for the original problem-- horse who runs the fence line:
I have had some success in a few cases. My upper level mare used to live outside (big field, shed, lots of grass) with several broodmares. As the broodmares got close to foaling, they were brought in at night, leaving my mare all alone. Some days she was totally fine with it, other days she would trot the fence line for an hour. Not frantic, screaming, stupid running, just that relentless jog, “YOU FORGOT ME, BRING ME IN!”
I’d watch her from a distance, and if she didn’t settle in 30 minutes I would go catch her and tie her to a fence post. Once tied, she relaxed and stood calmly. After 5-10 minutes, I’d untie her and get her eating-- either a little extra grain, or take her to the grass or hay. Tying her up was like hitting the “reset” button, and when I got her tummy to take over her brain, she completely forgot about running the fence.
Another OTTB gelding came to me from a training center. He was used to 1-2hrs of turnout in the morning, then coming in. My routine is to turn out at night. He would be fine until breakfast time. As soon as he saw me in the barn area, he’d start pacing the fence. Sometimes just walking, other times galloping and sliding at the corners (the WORST!). I’d rush to get their breakfast made up, and then bring him in first before he did too much damage. I tried hard to bring him in when he was quietly waiting at the gate-- before he got worked up and running. If he did run, I was very demanding of his obedient, patient manners when walking in to the barn. I wanted him to learn that patience got him what he wanted, not stupidity. It took 2-3 months, but now I’m able to bring him in at my convenience, first or last of the morning. He still walks occasionally, but the stupid-running to come inside seems to be over.
When I managed a TB breeding farm, we had several young fillies come in fresh off the track. Most of them were put outside immediately with buddies; if not 24/7, at least 12hrs in, 12 out. Some walked and paced, but unless they were truly dangerous (attempting to crash the gate or break the fence) we left them out. That was very rare. Most of them went through a week or so of adjustment (“I’m a racehorse! I need a stall!” which we ignored), and then they were back to being normal happy horses living out. They were treated like broodmares, not pets, and they learned quickly to deal with the great outdoors.