Dont build cities close so that the city borders will activate the monsters.
Which is a bit of a catch-22 because the AI doesn't follow the same 'rules'.
You're stuck with losing a city location to the AI's sub-optimal choice to which the monsters are released and they ignore the AI and come at you....OR you build the city so that the AI cannot to which the monsters are released and they come at you anyways.
I know I know....apparently the monsters aren't programmed to pick on the player.....but in my recent game with Gilden, when the AI Alter player builds a city RIGHT beside 3 DEADLY encounters.... 1 Storm Dragon and 2 Shirll Lords ... that ALL 3 ignore the Alter city and head STRAIGHT for mine 10 squares away....I really REALLY begin to wonder....