I had to bite the bullet, like Wardy, and dig a trench all the way round, I have large plot too. I'm just about to trench a new bit. It took a while, but for several years now, have had no bunny probs at all...had slugs, snails, aphid, pigeons....but no bunnies... ;D ;D ;D
Oh yes, and be warned, when typing bunnies, remember how close the n is to the m........ :o