This form of memorization take time and concentration. Lots of both actually. Rockefeller probably got closest to my personal style. This is also why it may take a couple of hours a day working on one song to get it down. Personaly, I never wrote anything down, just practiced a piece over and over. When I started playing, 1958, instrumentals were big (think Ventures, Duane Eddy, etc) and I would learn a song, play it over and over, and get it into my head, and hands, so that I could perform it perfectly. Then move onto the next. The guys, that I knew that were writing it down, always had to rely on their notation. But my plans all along were to play with a group, so any form of notation was out. I'm just saying that you probably have to push yourself a little harder and concentrate on nothing but your playing. Once you get used to commiting each song to memory, you'll wonder why anyone would do it differently.