Electric fences typically put out a short pulse at about a one second interval. With modern electric fence energizers, those with electronics in them, if the energizer thinks something is touching the wire many models increase in agressivness, so the fence is still effective despite much of the charge being bypassed to ground through foliage or whatever.
Voltage can be in range of a couple of thousand volts to 10KV, or for really big units 20KV. Big units can run many many miles of fence, providing the insulators are all present and the fence doesnt have grass touching it.
You need a decent ground rod where the energizer unit is.
The NEC doesn't cover fencers as they are an appliance. Some dont even plug in to mains, they run off batteries, sometimes solar recharged. If you have a fence in poor condition and the energizer is getting all agressive then the battery life is substantially reduced.
Electric fences can play havoc with telephone services.
One for Marc - there are some special funky intruments one can get for testing and locating faults on electric fences, some of which appear to work by black magic. Of course, some old timers just grab the fence to check its working or touch it holding a long blade of grass as a resistor.
Of course, the electric fence was invented in New Zealand, we do extreme sport and extreme fences

Many countries have limitations on electric fence power, but we dont...
My missus has sampled an electric fence and informs me they hurt. She certainly yelped and jumped when she touched one by accident...
Electric fences kill. A single belt wont, but a trapped animal will die. So probably would a trapped person.