Since they are a guarding dog, does that mean they lived outside with the flock of sheep?
You are thinking of a flock guardian. Breeds used for this type of work include the Great Pyrenees, Komondor, Kuvasz, Anatolian, Maremma & similar dogs. This type of work requires a different temperament than herding does: herding dogs want to boss stock around, whereas flock guardians live with the herd as a member of it. I have heard of Briards occasionally being tried as flock guardians but they seem to have been less than outstandingly successful at it.