In my current game, I am across a chanel from Torky. (Huge Marathon Continents) The Map has a one tile wide "ocean" running east-west for about 20 tiles I'm north and Torky is south. My boarder has his port shut off , along with the entire distance of this "chanel" and he is building his twentieth (or so) Galleon in his only port city with no way out. I wish there were a way for me to 'roll back' my boarder for a couple of turns so I could fodder more XP's for my navy