We've never had luck keeping in ewes with electric fences.  Once the nose is past, they are gone, and worse, the wool wraps around the fence and not only insulates it, but marks the spot for them to go through next time.

The only place electricity has worked for us is using a Koehn Drive Thru electric gate in the yard, and then only for the ewe lambs.  It takes them all summer to figure out they can get thru and by the next year they are in with the older ewes and the next bunch of lambs starts out.