You can get an Ernst water rudder at your favorite local hobby shop, or from Tower, or other mailorder places. There are MANY ways to hook one up, but remember you drive it from the rudder servo or at least from the same channel, and it goes the same direction as the air rudder. I like to attach fishing line to my rudder horns, go forward, down along a strut, then back to the water rudder. You have to cross the lines once to get the direction right.

Yes, you can just use a wire attached to your rudder. Clean and solder a piece of tin can material to it. NOT aluminum-has to be steel, and use acid flux and silver solder. The rudder should stick down about a half-inch lower than a straight line drawn from the bottom of the back half of your floats.

If you don't have a water rudder, you can still fly. My personally engraved block of granite says:"If your motor is running you can turn with the air rudder. If your motor is not running...it doesn't matter"