Guys, please!
If I understand the OP, you're suggesting the sheep carries the shocker device, yes? With a visible or invisible fence.
To be frank it churns my stomach. But that aside, my thoughts:
It's harder to change a battery on each sheep than to haul across one car battery every so often (conventional electric fence).
How would you check the battery life on every animal?
The sheep will be more prone to losing the collar/anklet/losing connection/battery draining etc.
If fence is invisible, they lose a valuable cue as to where they should/shouldn't be...sheep being mainly a "visual" animal this isn't fair. If you were training *blind* animals, then audible cues would be better. So if you were to move the invisible fence, how would they know?? If they have been trained correctly then they would effectively be hefted to that first pasture.
The shock could become associated with all sorts - like with the dog examples.
If an electric fence short circuits or goes faulty, you get scorched grass and loose stock. If a collar shorts you get a horrendously painful experience for the poor critter, if not death.
I'm out...