Briefly...
Unrest goes up when you blood hunt, set taxes above 100, have a battle, have certain bad random events, have an enemy spell, have a spy causing unrest.
Unrest goes down when you patrol, set taxes less than 100, have certain good random events. Maybe a few more for taking it down, but preaching doesn't do anything either way.
As you saw, blood hunting will jack up the unrest, so you either need to patrol along with your blood hunters, or just drop the tax to something (zero even if you are really looking for those chicks) and not worry about your income from that province.
I prefer to use taxes to offset rather than patroling, but that's usually because I can't seem to keep a patroling force away from some hot spot on the front lines
