Using llamas as livestock guards in North America began in the early 1980s, and some sheep producers have used llamas successfully since then. Some would even use them to guard their smaller cousins, the alpaca. They are used most commonly in the western regions of the United States, where larger predators, such as coyotes and feral dogs, are prevalent. Typically, a single gelding (castrated male) is used.

Research suggests the use of multiple guard llamas is not as effective as one. Multiple males tend to bond with one another, rather than with the livestock, and may ignore the flock. A gelded male of two years of age bonds closely with its new charges and is instinctively very effective in preventing predation. Some llamas appear to bond more quickly to sheep or goats if they are introduced just prior to lambing. Many sheep and goat producers indicate a special bond quickly develops between lambs and their guard llama and the llama is particularly protective of the lambs.

Using llamas as guards has reduced the losses to predators for many producers. The value of the livestock saved each year more than exceeds the purchase cost and annual maintenance of a llama. Although not every llama is suited to the job, most are a viable, nonlethal alternative for reducing predation, requiring no training and little care.
Give me the TLDR on using llamas to guard my livestock.
TLDR: LLamas can be used as livestock guards. Typically a single castrated male is the best choice (multiple males will bond with each other instead of bonding with the livestock). Generally llamas are cost effective, require no training and little care.