The ancient Tibetan Mastiff is the ultimate guard dog. It is watchful, aloof, imposing, and terrifying. These thickly furred giants are peaceful and laid-back indoors, lovingly devoted to their family, but distant and protective of outsiders. An invader up to naught good coming face to face with this old behemoth will probably move on to easier pickings. TMs can weigh well over 100 pounds and stand 26 inches tall at the shoulders. Although it’s impossible to talk about this breed without using adjectives like “powerful,” “muscular,” “massive,” and “substantial,” TMs are surprisingly agile and nimble on their feet. The large head projects a noble, sage expression with its high-set, V-shaped ears, and expressive dark eyes.