Recently, we have acquired several llamas. We've read that llamas are very effective at guarding sheep and goats from canine predators, but less effective against mountain lions. Consequently, we've limited our use of llamas to areas where we feel that mountain lion predation will be less likely. So far, we've not lost any animals to predators when they are guarded by llamas.
The advantages to using llamas are several. First, they eat the same feed as the sheep and goats, which eliminates the need to feed them daily. Second, they don't bark, which tends to improve relations with neighbors.
Despite these advantages, I still haven't established the same trust in the llamas that I have in our guard dogs. I guess the llamas will have to demonstrate their ability to protect our stock over time. I think I'll also need to evaluate the economics - can we afford to have slightly less protection if our livestock guardians also require less labor and have lower feed costs? I'd be interested in other perspectives!