Alpaca

In the United Kingdom, alpacas are sometimes used as pasture guards.

An excerpt from the article 18 facts about Alpaca

Although they are rarely aggressive, they are attached to flocks of free-grazing sheep, where they will defend the sheep from possible predators. If the herd is threatened, they are able to charge at an attacker and scare him off with their stance alone, as they are not equipped with horns or sharp claws.