Physical security is the primary concern. If access to data "after the fact" is what you're really asking, then you use the strongest encryption possible (a fe

Physical security is the primary concern. If access to data "after the fact" is what you're really asking, then you use the strongest encryption possible (a few options), and have a deadman switch to physically destroy the hardware (e.g., melt the platters/chips) including any caching mechanism(s) that's off-drive.