Problem: Optical media like DVDs eventually die. Solution, according to Barry Lunt: Actually carve data into a disc composed of magic hard "persistent" materials with a laser.
His Millennial Disks (say that 3x fast) can be read in regular DVD drives, despite being made with a secret sauce of "persistent" materials—he drops words like gold and obsidian, which makes it sound expensive. Indeed, they cost $US30. For DVDs. That you can never rewrite. A Blu-ray version is in the works (will they cost $US100?).
And it might be a lie! The plastic—his discs' weak point, your discs' strong point—could die before the disc reaches a thousand years old: "That plastic may limit us to a few centuries or a thousand years for now." Is there a warranty? Plus, shouldn't it be Millennial Disc, not Disk?
Also, will the slot-loading disc drives in the bellies of the invading aliens be able to read Millenniata's Millennial discs in 1000 years? These are the kinds of compatibility questions we should be taking seriously today, before they become a problem tomorrow, like with magnetic tape today.