Even better (for this goal, maybe not in general) would be some kind of "use it or loose it" provision. Your copyright expires after 20 years, or 5 years after

Even better (for this goal, maybe not in general) would be some kind of "use it or loose it" provision. Your copyright expires after 20 years, or 5 years after the last time your creative work was reasonably accessible to the general public, whichever is greater.