One way is to go back to the old US system, whereby you had to actively renew copyrights, and it costs enough that only active authors or publishers will do so. In reality, it was pretty messy, and there's a lot of arguing about whether a magazine copyright that wasn't renewed causes a story published in multiple places to have a lapsed copyright, etc etc.

It was also extremely painful to search for renewals until all of the renewal records were digitized by the Project Gutenberg Distributed Proofreaders. Now it's just moderately painful, because you have to be alert for variations in titles and author names.