The cure for the problem is to make a new rudder or modify the original one. The goal of the new rudder is to move the area forward so that there is a little area ahead of the axis of rotation. The second goal is to make the area larger. This is best accomplished by making it about four inches longer.
If you are making a new rudder you should use a hardwood and give it a streamline shape. There is still some discussion whether the bottom should be square or whether it should have the curve of the original. Below is a drawing of a modified rudder. This rudder has the pivot hole moved up in the aluminum channel and is longer. You can also see that the top is notched out so it is further forward (balanced). There is also a picture at Http://www.mv.com/ipusers/whale/g1rudder.html
Several people have modified their rudders instead of building a new one. One procedure is shaping a piece of wood and then fiber glassing it to the front of the rudder. A second way is to use "Bondo" to add to the front edge. a Third option is just using glass to reshape the front. I think the complete new rudder does it best but the modified ones certainly help a lot.