Is it broken to ferrets because if it isn't you will have to break it, i normally break my dogs to ferrets inbetween 6 - 8 weeks by letting the ferrets and pups run around together, then get them drinking milk out of a saucer together. When you take the terrier out let it mark a working rabbit sett and put the ferret in and let the terrier see the ferret working as it will help build up the bond between them. Good luck with your ferreting mate