First ask yourself a couple of basic questions:

1. Where will this horse be kept?

Do you have adequate land in back of your house that is fenced off and protected? Ideally one horse should have just over one square acre of land to graze and move about on. More horses would of course require more land. How is the land fenced? Wire fencing isn't very adequate, for a horse can get his foot stuck in the mesh. Electric fencing is fine, but the fence can and does short out, and horses seem to know when a fence isn't charging, so they challenge the fence. Wooden fencing is stout enough, unless you have a 1,200 pound or better animal pressing against it trying to get to your garden, or the mare in the next field! T-Bar fencing is dangerous. I have heard multiple horror stories of horses being playful and rearing up and impaling themselves on the top of the t-bar. So if you do use t-bar be sure you cover, or cap the tip of the posts. The most ingenious way I ever saw of a covering t-bar was from a friend of mine, oddly nicknamed Bar-T. She has several horses and the top of her t-bars are set with coffee cans, full of pebbles and cemet. No horse accidents for her bunch! 2 acres is considered acceptable for a horse (unless you want a Draft) Anything over that is a bonus for the horse. 

If you are going to keep your horse on your property, there are several things I would highly recommend. First off get a very large magnet and drag your fields. You will be surprised at what you unearth. A lot of the older type farmhouses, the farmers used to burn their garbage in the middle of a field, and that leaves behind a lot of scrap metal that can make its way into your horse's foot.