mmkay. you got some senioritis dude. just check the specs on a gibbs ascender and you will find mention of 'rope damage'. not good. (dont believe me. do a google or sumpin).
and the fact is a gibbs ascender is 'spring loaded'.
they basically suck for climbing needs since they dont have a handle and they require two hands to get them on and off a rope. and backing up one with a knot wont prevent rope damages.
i dont understand reticence to believe that theyre dangerous. you guys got an extra chromosome or what?
as for old school self belay: two locking carabiners with the rope tied to each with a clove hitch. pull out slack and alternate locking biners as the route dictates. you carry the rope in a pack on your back and it aint a bad idea to be tied in to the end. you need two hands so this is better used for aid climbing.