I had a mini pin, and anybody who doesn't want to get a security system, should look into a min pin, she was 8 pounds of terror, and I saw her bully large dogs every day. You couldn't get with in 30 feet of me with out her threatening to rip your arm off and beat you with it.
It doesn't have to be a large dog, hell I kinda like my neighbors dog, a VERY old and grumpy lab, who hates about everyone (except his wife, him, and small children, yeah) first time I actually got to pet him was when he was making nice to my toddler (protective of the little ones too) Any ways the teenagers don't dawdle near my house cause old Rex runs them off, my dog isn't worth a damn, all she does is bark, which is ok, but it's because she wants to play, not protect...