Originally posted by HAHAHuH?:

tried using a raft? that's what i do. (only use i have ever had for the raft lol)

Raise the under water ground level, put walls ontop of it.
Quick heads up, enemies have no stamina so the will still swim around.

Hmmm... no, can't say I've used a raft. I've cheated though, by flying. Seems that'd serve the same purpose. As to raising the ground level, as I said, the first thing that ought to be there is pilings on which to place decking, from a construction perspective.