What would it take for there to be Mythic water?

Every guide I've read about a Mythic age naval MU is that it's great, but doesn't matter because water is already won by that point, I.E. the winner has covered the lake in boats so you can't build a dock.

Any ideas to fix that for a mod? An unpathable zone around a dock or immortal docks with a tower attack obviously would, but trying to think of something more elegant that would be a less drastic change and fit more seamlessly into the game.