I've tried 3 strands (and 4 strands) of polywire. It works well for the ewes (mostly), and for the lambs initially, but as the lambs grow they get wise to the fact that they can run at it at speed and get through it without being zapped. And once one starts doing it they all start, and then the ewes will follow too.
I'm thinking of trying tape this year (or tape and poly wire combo), as I have tape around my pigs and the sheep never go near that. Whether that's because of the pigs presence I don't know, we shall see

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