A dog for our cats

We would like to adopt a medium-sized dog -- sex, breed or mix immaterial -- for our cats and ourselves. We have two cats -- a feisty five-year old female Persian that barely weighs 7 pounds and a sweeter, more needy long haired male that tops off at 15+ pounds. Both cats were adopted at separate times and, while things were dicey for a while (the little cat is the alpha female), now they're fine together, if not bosom buddies. We've searched Pet Finder for dogs that get along with cats and have been surprised at the number of Siberian huskies that are listed. We know that there are no fast and true rules about choosing a dog for a household with cats, but we'd love to know what your experience has been and the kind of dog you might recommend for a retired but by no means inactive couple -- our yard is mostly woods and would be difficult to fence. Thank you!