Fence

A fence is a barrier built to decide where animals, people and vehicles can go. It does two rather different jobs, and a single run is usually built for one of them: keeping something out, such as deer away from young trees, or holding grazing stock inside a defined piece of ground so they can be moved from one patch to the next instead of standing on all of it at once. A fence produces nothing itself. It only changes where things are, so the grass or the protected crop belongs to the land it encloses rather than to the wire.

What the fence has to be is set by the animal rather than by a standard design. Cattle are held by four or five lines of barbed wire with the top wire at least 1.2 m (4 ft) up. A rooting animal goes under rather than over, so its mesh is buried about 25 cm (10 in) into the ground. Deer need woven mesh 2.4 to 3 m (8 to 10 ft) tall and can still clear it under pressure. The wire is tensioned to roughly a third of the load it could take, so it keeps some spring rather than a permanent sag.

Fences fail at their corners. Tension drags an end or corner post out of the ground unless it is at least 150 mm (6 in) across and braced along both lines of wire leaving it. Two slower clocks run underneath: the zinc coating on the wire, shortened by large temperature swings, salt air and burial, and the posts, which rot at the ground line unless durable or treated. An electric line works by surprise rather than strength, needs damp soil to complete its circuit, and stops silently in dry weather while looking intact. Upkeep is walking the line after storms for leaning or broken posts and keeping growth off any live wire. Plan too for what must arrive with the fence rather than after it: subdividing pasture achieves nothing unless stock water and crossings come with it, and those often cost more than the wire.