A No-Fly zone in my influence area, ie. a setting I can set in the Civilization Manager or elsewhere, that restricts entry through my territory by opposing races. Obviously, if they go to war with me this would be ignored by the warring race. It could also hurt relations with other races, a "- for Closed Boarders".
And I'd like to see a chance for a galactic wide no-fly vote in the United Planets council.