Get a good tape electric fence and put it on top of the tposts. Keep it on and unless you or your neighbor has very stupid horses, one jolt and they will stay back.
We had issues with the neighbors horses and mules breaking down our fence and one time they beat up one of our geldings. We finally got a good solar charging fence(which even worked during wyoming winters) and used tape on the top of the tposts... As soon as we turned it on, we turned the horses back into the pasture and here came the neighbor horses and mules. One mule stuck his head over the fence, got zapped in the head and ran backwards snorting. One gelding came up and stuck his nose on the tape, got the same zap. Only my mare was stupid enough to touch the white tape, it zapped her....... After that first five minutes, all the horses on both sides would stay at least 3 foot away from the fence, no closer. Could not even entice them with grain to get closer. As long as they heard the "click" of the fence, they never got close.
We could actually use the white tape elsewhere, like around the trees and the horses would not get close to the tape at all.