I'm a Newfie person, too... many breeders have the stipulation about contacting them first if the adoptive owner or purchaser can't keep the dog - but they also put in a clause about a large fee if the dog is found to have been sold or given away without prior notification. I'm not sure how enforceable it is, but as part of a signed contract, it should be binding.
Another option (may be too late if you've already agreed to give the dog to someone), is Newfie rescue. They have a very inclusive contract, they do home visits and have quite a thorough application process. Prospective adopters must have their application approved before they can even attempt to adopt a dog. Breed rescues are wonderful at finding forever homes for the dogs in their care. If it was my dog, I'd be lots more comfortable about the dog's long term future if Newfie rescue had checked out the dog's new home and approved it... If this is an option for you, go to the AKC website, go to the Newfoundland page, and click on breed rescue for contact info.
Good Luck to your dog!
