I don't have much experience with dogs, much less untrained off leash ones. One is pretty big (a lab maybe?) and always runs right up to me and my wife barking territorially whenever I'm out in my garden, and doesn't stop until one of my neighbor's kids comes and gets them. I've had dogs try to fight me before and they make me really nervous. I just want to touch grass :(

How should I be responding to the dog when this happens?