Here, I love them!
Where my horse is, we use electrified fencing. Thing is, the electrified metal wire is pretty small and almost invisible, so the hay strings are put all over the perimeter, to make the wire more visible to horses and humans.
With it I can also fence the "arena"; there is no money to put a real fence there, and the horse is used to see the twine on the electric fence, so anytime he sees it, he thinks it's electrified, and doesn't touch it. As cheap as a fencing can go, and easy to replace when it breaks.
Of course I can't keep the horse inside just twine if I'm not around; he'd notice that the electricity is not there, sooner or later. But for a limited amount of time, and while I'm there and making sure his full attention is on me, it really works.