My opinion, and obviously that of many others I have seen with large scale birds, is dual rudders. In fact look at full scale birds, they have 2.

Something I have also done with my planes is to set a second rate, if you have a tx that has adjustable rates, with max travel for low speed water travel. Once on step I flip my rudder rate switch to normal and away I go.

One thing I have not seen in r/c is rudders you can pull up??? Full scale you can/and do pull the rudders. Maybe I am missing something. I belong to a large float club and have seen a couple hundered planes of various set up's and never retractable rudders.

One thing that works great if you have a Northstar is to steer with the rudder and ailerons. The ailerons when deflected make great brakes in the water.

Have fun and happy flying.

ps. If you want a good picture referance go look at the forum FLOAT CUB PIX in the seaplane catagory

these guys have a bunch of scale pics and they look great.