As long as the dog stays in it's yard, the dog is fine. I have no fence, but my dog is under verbal control at all times. Of course, it doesn't hurt that he's scared of everyone, so seeing people sends him scuttling back to the door at top speed.
I would be very concerned about the dog being left unattended outside, though. There's too many things that can go wrong very quickly, and without the owner being a witness to exactly what happened, things can go ugly.