The large white dogs we have are Great Pyrenees. They are guardian dogs and are useful for keeping the coyotes at bay. They know the boundaries of their territory and protect it from predators. They know the difference between good animals (chickens, sheep, goats) and bad (coyotes, hawks, bob cats and mountain lions for instance). They are protective of their territory and will not let a predator enter. They need at least two dogs to be effective. While one dog will directly confront the "threat" the other will guard the flank. They are not easily frightened. In this picture, three Great Pyrenees are letting a bear know that it is not welcome.
These dogs are passive guard dogs. They will not attack the predator unless forced. Instead they bark and advance slowly, waiting for the predator to "give up" and go away. When people or dogs walk past our property, our dogs will bark to inform the outsider that this is their property and that it is their job to guard it.
We also keep guinea fowl as guardian birds. Like the Pyrenees, the guinea fowl will confront predators. They align against the threat and make loud "kacking" noises. They work with the dogs. I have seen the guineas directly confront a coyote and keep the chickens safe. The noise alerts the dogs who work with the guinea as a team.
Our dogs are very gentle with people they know. They are especially good with children and elderly. However, they will not let a stranger on to our property. When you see our dogs and guineas working on our property, you know that they take their job seriously and are trying to keep our farm community safe.