I have used electric fencing for several years now. While the perimeter is not electric fencing the interior fence lines are. The fence runs along a long driveway on both sides and down to the barn. My horses have not gotten out in all this time, even if the fence is down for a short period of time. "KNOCK ON WOOD" of course.
If you are having a problem with your fencing, make sure it is up and running and lead your horse up to it, and touch their nose, chest to the wire-some part of them that will feel the shock, even if you have to clip them in that area. They will learn to respect the wire then and pass the information along to the others
I hang long strips of duct tape off the top, middle, bottom of the wire in various areas on the fencing. I make the strips long enough that the wind/sun catches it - makes it move so that the horses can see it and know the wire is there. Perhaps they cannot see the wire?
When I test my fence with wire tester, it tests 2000-2500 volts. Do not know if this is high or low but it keeps them in.
I used the
leading up to the wire fence - for dogs that do not realize the fence is on or that their coat is too long for it to shock them. Make them touch the wire and they will go into the pastures anymore - and they don't. We are not in the same kind of weather as you and do not have snow on the ground like you do. I have had my fence quit during the summer months due to the ground being so dry, even with 7' of ground rod buried into the ground. I just run a hose down next to it and run the water slowly and the fence will begin to work again.
Do you run at least two wires of fencing? I was in sand and had to use two wires to get a ground on the fence for it to work. I also used the colored wire at one time, yellow and black twisted wire. That wire requires a pulsating charger and mine was not. It eventually burned the wires so the fence would not work - in several places and not all at the same time either. It was hard to detect where the problem was, so I replaced it all with 17 guage wire and the ribbons of duct tape I am telling you about and have had no problems since. Only the typical upkeep of the fence to make sure the horses or dogs have not knocked the bottom wire loose for whatever reason and have grounded it out.
Good luck, hope this helps.