wire is safer but more expensive than strands of smooth wire. It is more difficult to install, and has some visibility issues, but horses are less likely to become tangled in it or be injured if they run into it. Adding a top rail of wood or synthetic material increases visibility of the fence and prevents it from being bent by horses reaching over it. A strand of electric fence may also keep horses from pushing on a mesh fence. Mesh fencing needs to be heavy-gauge wire, woven, not welded, and the squares of the mesh should be too small for a horse to put a foot through. "Field fence" or "no-climb" fence are safer designs than more widely woven "sheep fence." Chain link fence is occasionally seen, but horses can bend chain link almost as easily as a thinner-gauge wire, so the additional expense is often not justified by any gain over good-quality woven wire. Electric fence comes in many styles of wire, rope and webbing, and is particularly useful for internal division of pastures. It carries only a mild charge that causes a noticeable shock, but no permanent injury to animals or people. It is relatively inexpensive and is easy to install, but if electricity fails, it is easily broken. It is excellent both as a temporary fence and, in single strands, as a top or middle barrier to keep horses away from conventional fencing. There is some danger that horses can become tangled in an electric fence, though because the materials are finer, it usually breaks, stopping the current, though injuries are still possible. Because electricity can fail, it should not be the sole fencing used on property boundaries, particularly next to roads, though a strand on top may be used to keep a horse from leaning over a fence made of other materials. Nor should it be used alone in small pens where horses may accidentally bump into it on a regular basis. However, small single-horse enclosures are sometimes seen at endurance riding competition, where temporary fencing must be set up in remote areas. In residential areas, warning signs should be posted on any boundary fences with electrified sections to keep people from touching the fence and accidentally being shocked. Wood is the "classic" form of horse fencing, either painted planks or natural round rails. It is one of the safest materials for containing horses. Wood