I was recently reminded of the childhood naval game Broadside. As the defender, you get to place four shore guns and six mines during the setup phase, one on either side of two channels. 
The channels are choke points that the attackers ships have to pass through to be able to win the game; one is close to the attacking fleet starting location and represents a direct path to the merchant ships they need to sink to win the game, while the other channel is out of their way.
The trick is that two of the guns are useless decoys, while the other two get a free shot on any ships that passes within range, and three of the mines can destroy an entire ship, while the other three are duds.
Does anyone who remembers this game ever develop a strategy for how to place these static defensive units, and if so, how did that change how you deployed your blue fleet once the game started?