I would make things very very simple.

Barbs only attack people who attack them first. (this means newbs who don't want to fight them, don't have to)

They will randomly counter attack 3 times during the next 7 days. And then stop until you hit them again.

They will only attack if they know it will actually hurt you (they will know if you have gates closed and such). That means they may attack and lose, but they won't suicide against you. They'll only attack if they can get some good damage on you. Maybe they will save their "3 attacks" into 1 big one if you're too tough.