They were driven away by a dog because the dog wasn't the one attacking them in their own settlement. There's a big difference between them coming at us, and us coming at them. In the former case, we force them to decide who among them will be the first up the metaphorical ladder. In the latter case, we're the ones climbing the ladder, and they're the ones dropping rocks and boiling pitch on us.
Our best bet, IMO, is to give them three options: 1. negotiate with us, 2. snarl at us threateningly until we go away, 3. fight us.
An unprovoked attack would give them one option: 1. fight us.