Here in Wales any sort of collar that may be able to give an electic shock if set in that mode or adapted to it is now illegal be that for cats, dogs or stock it was brought to law by massive pressure from many animal welfare concern groups and met no opposition from the occupants of " The onion house " when they debated and passed the law.
The RSPCA type orgs also take a very dim view and a robustly strong line against electrocuting an animal into compliance and are happy to prosecute those who use them under the cruelty to animals legislation .
Me .... I'm not so squeamish and think in certain circumstances it may well be a sensible thing to use to bring an animal under control if it is done under supervision , but I'm not sure it would be the most effective solution for stock even if it was just an animal audible sound sent by radio/ infra read triggers etc. .
One thing that may surface in the future for cheap invisable stock containment are the directed ultra sound / micro waves that make things hot currently being used/ tested for crowd control rather than possibly leathal stun grenades & rubber bullets etc.
I saw a guy on a sky discovery weapons prog have to leg it away from a test dummy to a determined direction when exposed to a sound beam from over 200 mtrs away . Apparently they have been used in Iraq and Afghanistan to break up violent crowds & keep them apart .
This new battle field weapon may well be a fence for the future