Use a high energy laser to etch thick platinum CDs. The pits produced by the laser should be deep. Coat the etched surface with a thick layer of diamond using v

Use a high energy laser to etch thick platinum CDs. The pits produced by the laser should be deep. Coat the etched surface with a thick layer of diamond using vapor deposition. Enclose the CD in a vacuum case made with extremely durable material (granite maybe). Entomb the CD case in a 10 ton cement block. Stack the Cement blocks (if more than 1 CD) in a shape of a pyramid on a dry desert plateau. Irradiate the area around the pyramid. That should last more than 50 years.