Paul Kenny explains the Outer Rim Delay.
In this trick, you nail delay the disc on the outside of the rim. The only more difficult nail move I can imagine is a rim delay on the top lip of the disc. Anyhow, the wind can be a key factor so be sure to face the wind before you start. Then give yourself a ton of spin. Rim delay the disc so the nose is up into the wind. With your other hand put three fingers together so the finger in the center is slightly lower than the other two. Now place your nails against the outer rim. The disc should ride in the grove created by your fingers. Try to balance it there and chase after it if it begins to fall. Note that your nails will be between 6 and 7 for clock or 6 and 5 for counter.
Once you feel comfortable with this, try landing the outer rim delay from an airbrush or off of an skid or other restricted angled set. If you can pull that off you will be one of maybe five people in the world who can, and that deserves a 10 on anyones judging sheet.
By the way, does anyone know if this move has a more official name?