The cable idea has too much play in it, and even if you get it right, they still move all the time, and in time, the problem will return. If you want it rock solid, you either need to create a very solid truss along the top, or brace it from below.
I like Rockytoppers idea, but don't know how big, or what size material you will need to make it work. Too small and you wont accomplish anything. Too big and you risk either making it too heavy for your cantelever, or you waste allot of money on material.
My first thought was to attach a beam, or support to the footing and 2/3rds out on your pier, to create a large brace. Basically support it from underneath.
Somewhere, you need to create some triangles to lock it all together. Either a very large one at the bottom, or allot of smaller ones on top.
Eddie
