In Burma they record valuable teachings by carving them on marble slabs. Stone inscriptions can still be read that were made thousands of years ago.
When cassette tapes became cheap and popular, all talks were recorded on cassette. They soon found that these deteriorated within a few years, so started transferring them back to reel-to-reel tapes. Now they are transferring to CD, but like you, I expect they will soon fine that tape is actually more reliable.
Tape backup might be more reliable than CD, but still not 100% guaranteed. Whatever media you use, the most reliable method is to make two copies, store them in different locations, and refresh one copy on new media every two or three years.
Statistically, though any media is certain to fail at some point, the chances of two copies failing simultaneously is approximately zero.