Underground Electric Fences?

Via Washington Monthly, Rand Paul is proposing an underground electric fence for the Mexican border.  Now I'm guilty of assuming that I know what "electric fence" means, so I'm laughing at the suggestion.  Back when I was a boy, an electric fence was a single strand of barbed wire, strung on ceramic insulators attached to metal fence posts spaced maybe 10' apart, which served as a temporary fence to keep our cows in the meadows.  Instead of going for multiple cuttings of hay, which on our soil and in our climate wouldn't happen most years, after we hayed the field, and the grass got a little regrowth, we'd turn the cows into the meadows. The "electric" part was that the barbed wire was hooked to a jobbie (I forget the precise terminology) which put an intermittent low voltage electric charge on the wire, giving a sufficient shock to any cow to deter them from pushing the fence over.  A problem with the fence was that it could be grounded, if something (weed, brush) laid against the wire while still connected to the ground.  Thus "underground electric fence" seems to be an oxymoron, but I'm sure Dr. Paul has a reasonable explanation.