I decided to use a skeg shaped like the one describe in the June 1995 issue of Sea Kayaker, but I wanted to make it self-extending so I wouldn't have to "push" a cable to extend it.  I also wanted it easy to service in case it ever needs to be replaced. 

To begin, I made a mockup of the skeg and its controls.  This allowed me to play around with pivot points and bungee anchor points until I found a configuration that worked well.  I cut a test skeg from lauan, and used a scrap piece of  wood clamped to my workbench to act as one wall of the trunk.

Initially, I used the center of the skeg's semi-circular top edge as the pivot point, but I wanted to to make the skeg easily removable by using an axle slot.  A slot all the way to the center would weaken the skeg too much, so I moved the pivot point closer to the edge.

The dowel close to the spring clamp is functioning as a stop-block.  The final skeg housing will have a different style stop-block that will also function as an anchor point for the bungee.