I'd say, dont be to hastey, go back and tell him, your happy to pay a fiver, but you'll need a permission slip, you can find one to download from this forum, make sure it has his name/address/farm name on it, do a days ferreting one saturday, then on the sunday, take a trip around all the other surrounding farms, rather then just knocking and asking for permission, you can knock and say
sorry to disturb them, but you have permission on mr so and so's land, but a few of the warrens pass over the boundary fence, could you get their permission to cross the boundary, having the permission letter,