Geko is one of the best shooters I've met so far. His designs and shooting style have been highly influencial to my own - in fact, I use a slinshot made by him in tournaments. It is well worth having a look at his slingshots, even more at his Youtube Channel, where a lot of instructional videos can be found.
One can divide his slingshots in two "Generations". At first, he used big-diameter tubular bands and tried to increase accuracy with stabilizers and rotating forks. The second generation starts when he realizes the advantages of flexible attachements, flatbands and small-diameter latex tubing (more about that in the Power" section), which results in some excellent designs.
First Generation
Second Generation: Board cuts
Second Generation: Metal / Fimo slingshots