Simple Electric Fences
The simplest kind of electric fencing is the kind often used as anti-raccoon measure for gardens. This consists of a single strand of electric fence wire 4-6 inches off the ground. Aluminum fence wire is best. A second strand 10 inches off the ground will help, though it is often not necessary.
It surprises people that such an electric fence will keep chickens in and predators out, but it works! It helps that predators generally sniff at anything new they find, so they will get their noses zapped by a fence wire they could easily step over. That's generally all it takes.
Sometimes chickens will learn to get past such a fence, especially if they are tightly fenced or run out of feed frequently. But they are ideally suited to giving the chickens acres of space, something that simply isn't affordable with other methods.
I read about this type of fence in a 1960 article about raising pullets on free range. Like many excellent techniques, it was forgotten after the industry shifted to confinement.