All dogs can be guard dogs

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You'd think these dogs would just be snacks, but clearly they do an excellent job of scaring the bears away. As the saying goes, it's not the size of the dog in the fight, it's the size of the fight in the dog - and these little dogs have a whole lot of fight in them. They don't even really need to be able to take on a bear in an actual fight, simply raising the alarm can be enough to protect people all on it's own. 

Of course, just because all dogs can be guard dogs, that doesn't mean they all are suitable as guard dogs. Not all of them have the right temperament for it.