NT "The world is full of urban myths", I'd apply a bit of common in this case. Ferret out all the burrows thoroughly using Hobs or Jills, then lightly plug all of them up with soil. If they are then reused you should then see where they are to be Ferreted again. Obviously I don't know how big your mates farm is and how much time you have on your hands, buy I would try this method first.
Also you mentioned about neighbouring livestock and not being able to use dogs, aren't the stock fenced off from your Farmer mates land? Do you not have/know anyone with steady enough dogs to get on th