We have goats on our lease. There is one that guards them. Cool dog, playful as hell. He is a lot bigger than in the pic, probably 100 lbs. Do they have to be trained or is it a natural thing.
The drive to protect is a natural thing.
You have to train them to protect what you want.
They have to be "bonded" to their flock....whether it is humans or gerbils or sheep.