Yeah, you've little hope I think with lambs. I tried it myself and got each of them to zap themselves on the nose when they were young - that kept them in for about a week, then they just started charging the fence. To them it's just a gap that they can see that they can get through, so they go for it. You could try more lines at a low level - say 6? I've tried 4 (up to thigh height) which wasn't enough. And maybe use tape as that has more of a physical presence? (but produces less zap)