As I stated in the thread on landmines, you shouldn't add a new aspect to the game unless you add the accompanying counter-measure to it. Also, sea mines typically were laid in shallow or otherwise constricted waters (near potential amphibious assault beaches and harbor approaches). The reasons are because they are typically moored to the ocean floor to hold them in place; otherwise they potentially pose a threat to friendly units, and such a threat would be totally random. They were used both offensively and defensively, by the way. The counter to mines or course is mine-sweepers. There was also special rigging some ships could deploy that was designed to either pre-detonate the mines or push them aside so they could not contact the ship's hull. None of this is modeled in the game, and to add the mines without the counter-measures would be detrimental to game play, IMO.
