I would have told your dad to pound sand. Dogs that leave their property are fair game; if he doesn't want the dog to suffer any ill, he should keep it in the yard.
Our house on one side of the road, barn and farrowing house on the other and a T Road to boot. No such thing as keeping it in the yard. You train it to not chase, which he did, and to stay off the road if there are vehicles. I personally thought the guy was going to get his head caved in by the old man for smacking a pup that at that time wasn't even 4 months old yet. I guess the point of my story, was you have to use common sense and determine if the dog is truly a threat.
I don't begrudge you the right to protect yourself or your wife. Hope it didn't come off that way.