I built my own and it's not that big a deal. I got ideas from a couple of places and mine has worked perfectly all summer. But I have rarely needed it.

http://www.kudzupatch.com/boats/projects/hull/index3.html

Click on the second photo down. You can see mine. I would only make one small change on the next one. I would move the line on the skeg further back. That would give me more travel on the line and I could adjust it's position finer. I could put a jam cleat but I hate the looks of the plastics ones and my wooden version just never would hold the line well.