I pride myself that I've managed to get my sheep down to 2 strands (used to be 6! I had a determined escape artist who soon learnt manners!)
I have some Wiltshires and use polywire, they seem to know when they are close, but the cretins don't go hungry here.
All 12v fencers, newbies I train on a powerful one, before dropping down to the lower power ones that have good clicks!
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I also find it quite humorous when some idiot very slowly touches it with their nose, yelps, then goes back for a 2nd attempt! (A calf did 4 attempts before he got the jist!)