A perennial question is asked and often requires a careful review. An answer is not always that simple.

1/. Horses are Gregarious animals and are naturally inclined to seek other animals to create a herd. This is not new and has been bred into them over centuries. Horses are prey animals and the best method for them to evade being eaten is to form a herd. 

If a horse is kept on its own and other horses are visible or may even only be heard and smelt, the horse will accept a considerable amount of pain to get to his mates. The only solution to this is to get him a buddy - does not always need to be another horse.

2/. The quality of the Electric Fence. The fence must be running in the region of 5000 volts otherwise the fence becomes merely a tickle to the horse. A tester is vital to get an accurate assessment. Using a green leaf is not nearly accurate enough. Don't ignore the earth stake - many problems with a fence emanate from poor earthing.

3/. Baiting the fence. This is by far the most effective method of curing a fence-jumper. Attach a small succulent bait to a high energy fence and the horse will lick it with his tongue. The tongue is wet and has a huge number of very sensitive nerve endings so he/she will get a very strong imprint on his mind that this fence will hurt. This is particularly useful when first introducing an electric fence to an animal. There are numerous reviews saying this works. 

Does Baiting a Fence Work.

Development of Baiting an Electric Fence.

It is not necessary to continually bait the fence, as soon as the objective has been achieved then stop and only resort to it if the issue re-occurs.  

The height of the fence is actually that critical, as long as the top wire where the bait is placed is about the height of the targets nose so making it very easy for him to access the bait is all that is required.

Baiting has spread around the world and is used with a wide range of animals.