I looked into the 'invisible fence' idea when I started keeping goats again, it was used succesfully in america, collaring a few members of the herd, to clear scrub land.
I planned on using it to back (front) up sheep netting, I wouldn't use it AS an invisible fence, it wouldn't be fair if they weren't sure of the boundary. but the advance warning bleep as they got say 2-3 metres from the fence should have been enough after a few attempts. the 'shock' can be adjusted, as can the distance warning. I planned to run it along the fence posts rather than bury, then I would still be able to move it. I ended up going for a normal electric fence.
Seeing and hearing my goats cry and run when they first touch the 'standard' electric fence was heartbreaking, but it had to be done for their own sakes, or they would have to be tethered (one was cheap because they couldn't keep her in).
This is goats, don't know about sheep, or pigs, but the 'unit' on the collar looked quite clumsy.
I think the abusive 'guest' just came in to stir us up, we should ignore such idiots, they thrive on upsetting genuine people
