By "anything special about the water . . . " I was thinking of stuff like shoal water or rocks that would need a flip-up rudder, a sandy bottom that could gum-up a complicated retraction mechanism, or dense weed that can wrap around the blade. I have all of the above where I paddle, so a tapered flip-up rudder with the hardware above the deck works best, ugly though it may be and sadly lacking in style. The taper lets the weeds slip off, the flip-up feature glides over rocks and actually steers well if it contacts the sand or mud bottom, and not much can reach the mechanics.

Oh, yeah....'all of the above' ;-)
For myself, I'd add to the list: 'Rudder blade self-protecting if kayak is beached without retracting rudder' ... not that I would ever forget, of course......