my grandad was a keeper, around the release pens, there were feed storage sheds,which housed several 50 gallon drums containing feed, which had tin sheets across the tops, every other week in at least one of the bins, would have a handfull of rats that had dropped in after there lunch, he believed that dropping first attempt terriers in and having ago always payed divide ends, being right on top of the job always got them goin! one of his older dogs he had, russell x westie was mustard at this close encounter mayhem!