I had this exact scenario play out, and it was also in the White Mountains. The dog was about the same size, probably a bit smaller, but it was acting very aggressive towards me and my daughter. The owners were nowhere in sight. I tried to get the dog to back down but it wasn't giving an inch. I had positioned myself between the dog and my daughter and I truly thought it was going to attack. I had my knife out and I was ready to use it if he did. The owners finally heard me yelling at it and came up the trail and leashed it, but it was still pulling at the leash and baring it's teeth. I reminded the owners of their responsibility and let them know that I wouldn't hesitate to have killed their dog if it attacked, and that if their dog did that to someone that was carrying, there's a good chance it would have been dead by the time they got there.

I agree that it's generally the owners and not the dogs that are at fault, although this dog was particularly aggressive. I can't believe this is the first time that the dog had acted aggressively like this and the owners should know better than to let it off leash. Even if it hadn't acted this way before, the dog should be leashed so that it can be controlled. I believe the White Mountain National Forest allows dogs to be off-leash but must be under voice command at all times. This dog clearly wasn't under the owners controls in any way. They acted totally surprised that their little angel acted this way and kept saying "he's never done this before." Well, now that they've seen it for themselves, I hope the act responsibly and keep him leashed, for his own good.