No, use your head looking at warrens, any drains leave alone fullstop, or real deep looking holes.
Try the smaller warrens, allways in with a chance if things do get hard, use one ferret, better a jill to bolt, keep away from sight and try not to make to much noise and you are already lessening the chances of trouble.
Watch the dogs, most dogs can be usefull on a warren, there nose and ears are better than yours.
If you can get a locater it's good insurance, and morally right if the ferrets start killing down.