I think Tibetan Mastiffs are the best guard dogs. This bread endemic to Tibet is big and ferocious. Tibetan Mastiffs are popular dog breeds in Tibet, Nepal, Mongolia and India. The adult male can be anywhere between 45- 75 kg. Adult male measures 65-75 cm. They have long thick coat. Black is their normal color, and some dogs also have brown patches on their belly. They have big heads and long thick tail.
In the rural areas, Tibetan Mastiffs are generally used to guard sheep from wild animals. It is believed that four Tibetan Mastiff can guard the heard of 100 sheep. In the urban areas, Tibetan Mastiffs are used as night watch dogs.
Tibetan Mastiff are the dogs of cold climate, therefore, it will be very difficult to raise them in warm climate.