There is a rule of thumb that recommends never bringing home farm animals until you have your fences up. Safe, sturdy fencing is critical. For horses, electric fencing is often best, but you will probably find that you end up with a mix of fencing.
Electric fencing is probably the most commonly used for horses in the backyard setup. It is inexpensive, easy to install, and easy to move and reconfigure. If your horse has never been housed in electric fencing before, it is important to teach him about it. Usually, it is necessary for the horse to experience being zapped for him to get the idea that he needs to stay away from it. This may seem mean, but in order for electric fencing to be effective, the horse needs to know the wire means business. If horses have been fully introduced to electric fencing, you can generally feel comfortable with them behind it for the rest of their lives.
Several different kinds of fence wire can be electrified: barbed wire, twisted wire, flat tape, smooth wire, and high tensile wire. Forget about barbed wire for horses. Horses can get badly torn up when they get tangled in barbed wire, and it's just not worth it. Similarly, high tensile wire is so strong that it can literally saw through bone if a horse gets tangled up in it. Each type of fencing has its advantages and disadvantages to consider. Whatever you choose, it needs to be strong and highly visible to help deter horses from running through it.
White board fencing of the type that goes on for miles and miles in Kentucky racehorse country is beautiful, but painting and maintaining it is a high-maintenance chore. It is, however, one of the safest types of fencing available for horses, and that's why you see so much of it in Kentucky, where very expensive and valuable racehorses roam. Even board fencing that's left natural is expensive and time consuming to replace when the horses chew on it or kick it, which they will. People who use board fencing often add electric wire across the inside top to keep the horses from chewing or rubbing against it, so it becomes double fencing.
Vinyl fencing that resembles regular boards comes in two-, three-, and four-rail designs and averages around $4 to $5 per linear foot with posts included. Companies often offer lifetime guarantees against breakage. This kind of fencing is very durable and safe. It is advertised as a low-maintenance product and easy to install, but the initial outlay is considerably more than other kinds of fencing.
For small corrals, metal pipe panels that link together with pins can be convenient. The configuration can easily be changed and divided in new ways for different situations. Look for panels that are made for horses. There are some stock panels that have a vertical brace made of flat metal that can really cut up a horse's leg if it gets caught in the panel. Pipe panels suitable for horses usually come in eight-, ten-, or twelve-foot lengths and are typically five feet high.