The fact is that there is no good dock edge that I would tie to for an extended amount of time. The best solution is vertical posts covered in PVC to ride on the rubrail, but even that is not perfect... especially in an area with a lot of boat traffic or rough conditions.
For extended mooring, I love these: http://www.wakewatcher.com/
or setting a mooring off the dock and pulling the boat in as needed. For us, our waterways here are way too busy to tie a boat to the dock.