I have three dogs and one of them is a guard dog. Not trained that way, she came that way. It's her breed. We chose her because we admire the breed and we wanted a guard dog. I know, without a doubt, that she would protect her house, her people and the other animals if a perceived threat were to enter our house or yard. So yes, if she were in the backyard and some strange dog landed right in the midst of it, she would do what she felt needed to be done in order to protect us.
Now, it would be a totally different story if I or my husband were outside with her. Even though she is a guard dog, she is *gasp* trained and highly socialized. So before you go around calling our dogs vicious, unsocialized, unloved, uncared for, and untrained, I suggest you read a little about those of us that said Oakley would have been in danger had it been our yards so that you can be educated instead of insulting.
And as for your rude comment about guard dogs not generally being loved family pets and the asinine assumptions that an owner of a guard dog NOT join a dog forum... my vicious attack dog is currently laying at my side, with her head on my chest, snoring. Yup, that's right, this unloved, uncared for highly unsocialized monster is in our house, laying on my bed, snoring. The horror!