Fencing can be constructed of poles, pipe, boards, plastic or wire. Or the fence can be a combination of these fencing materials. Regardless of where you keep your horse, always be alert for loose boards, nails and any projections that could cause injuries. The important thing is that the fence be visible to the horse to keep them from running through the fence. Horse's normal behaviors can make "Horse keeping and fencing a real challenge."
Herd social pressures usually are to blame when horses challenge fences. Whether one horse is trying to escape another, or one is trying to get to the other--either way horses will get through the fence.
If your horses are kept in a corral, paddock or pasture with a loafing shed shelter, it is important that the shelter and paddock have enough room for the number of horses living together. Horses are herd animals and they establish social orders. Dominant (boss) horses bite and attack those horses that are lower on the pecking order. Be sure to give horses enough room so the horses get out of the way and hopefully preventing injuries.
If you have groups of horses sharing a fence line; then the best but most expensive fence is double fencing (horses cannot reach each other with a space between). If you have to use a shared fence lines then consider a strand of "hot wire" (electric fence) across the top of all shared fence lines.
Weanlings and yearlings tend to be playful and rambunctious and need to be housed in the safest, strongest fences you have.
Any wire fence should be smooth -- not barbed wire. Barbed wire injures horses. Electric fences should have smooth wire or it can be plastic coated. There are some great products on the market such as polywire, ribbons etc. that can conduct electricity. Make sure you buy a system (charger) that is large enough to put out an electric charge that can power your fencing design. Then regularly check the fence-charger to be sure it works. Most electric charges have a light that shows when there is a break in the fence or if the circuit is incomplete. Remove overgrown weeds from fence lines. Check all fences regularly and keep wire fences tight. Most vets report wire cut from fences that were not on or loose wires that are in disrepair. Whatever your fence types make sure your fence is properly installed.
The horse's eyes are attracted by movement; this makes a fence more visible by attaching strips of cloth or plastic along the wire. This will help introduce a horse to a hot wire fence for the first time.
Is your fence visible? Color is not a key factor in visibility to the horse, but brightness and contrast are. Where you place your fence also has a lot to do with how visible it will be to your horses. Remember that horses are far-sighted creatures which tend to look to the horizon. Placing a fence at the bottom of a hill, even if that's the end of your property line, might be is an accident waiting to happen. The horse will fail to see the fence until he is through it. Shorten your property line by placing the fence along the top of the visible ridge will help to keep horses safe.
Height - Install your fence at a height equal to the height of your horse's eyes with his head up, about five feet or better. Draft horses need something higher taller and miniatures or ponies with less. Most State's Laws recommend a fence at least six feet high for keeping stallions.
Your gates and placement of them are just as important as the type of fencing used. Place your gates so that horses don't get crowded when leading them in or out. Make gate opening large enough to get farm equipment through to work on the pastures. Fence off trees, power line guy wires, wet areas, streams, ponds or anything in which a horse can get in trouble. Avoid, using metal T-posts (metal stake posts). Horse can impaled themselves on a T-post. If you do use T-posts cover them with plastic caps on the tops to help avoid any danger.
Regardless of the material used for the fence, be sure to fasten the fencing materials to the inside of the fence. When horses lean on your fence, the boards, pipes, or wire will be pushed against the posts rather than off them. Boards on the outsides of the posts might look nicer, but can be pushed off--and the horses can escape.
Any fence type to be safe and reliable requires planning and proper instillation and may requires some professional help.