well it depends on the warrens, ferrets and whether the rabbits want to bolt, for example sometimes we have had to use 2 ferrets on a 10 holer because it was deep and the rabbits dident want to bolt and then on another occasion we have used 1 very good ferret on a 200 hole warren which was very deep but the rabbits were bolting very easy, so 1 good ferret was suffient.