As an addition to the ferret threads above, it's worth looking very carefully for seemingly unused holes when placing the nets, otherwise you send your ferret / polecat down and watch as piles of leaves erupt into running rabbits whilst your nets stay empty. You can also tie a reel of string to ferrets tail to "encourage" it out (note they don't like this very much), and avoid ferreting close to a road, tarmac is much more difficult to dig