pedestrian: I LOVE that idea - let the sea monster attack 1 square at random each turn.

One of the things I know I don't like about regular battleboats is it takes longer (many users like faster games), so having this 2nd square always getting attacked will also speed up the game. Plus like you said, for me - I usually follow a "pattern" to search for boats, and that would force me to adjusted continually during the game.