Mountain Dog is a label, not one breed, so a dog listed under it in Pine Bluff might be a Bernese-type farm dog, a Great Pyrenees-style flock guardian or a mix of the two. Most carry heavy bone, a thick double coat and a history of guarding or hauling for farm families.
Many are calm and devoted, but a guardian-leaning dog can be watchful and bark at night, which is worth knowing on a street with close neighbors. Their coats were built for cold mountains, not an Arkansas July, so a Mountain Dog here needs air conditioning, shade and a brush close at hand. Expect heavy shedding, a big appetite and the joint care any large dog needs. Size, coat and temperament vary more than the label suggests.