And I don't want copies backed up on cloud or via a wifi connection; it's too risky for the data to get lost or corrupted.
Actually, I'd say this is a much safer save options. If you only have a local copy, you have a single point of failure - you risk losing your work in the event of software failure, hardware failure, theft, fire, flood etc. Cloud save is available on any device and many cloud services also have built-in backups, e.g. restoring a file to any time in the past 30 days. If you have important work I'd highly recommend setting up at least a backup to a cloud service.