The solution is simple. LOTS of 'em. What was done before that is the grandfather. This way, if the most recent work gets scrapped, the most you'll have lost is a few hours of work. If son AND father get scrapped, which probably won't happen, at least you have grandpa to fall back on, and won't have to regenerate ALL of the material.
Diskettes are cheap, when it gets down to it.
How often depends on how often you change the data. Heavy editing can scatter the information all over the diskette. In time this can mean that the computer and drive will misallocate space, and the data will get lost in the shuffle. The IBM PC is a good example to use here. It has two basic methods of copying information.