Well, maybe I don't understand what you mean by "bitrot". GMR media doesn't "rot" in the classic sense of bits flipping over time (well, not in human-scale time), the way that happened with floppies and QUIC tape. If you're adding some new meaning to that term, you'll need to explain it.
But if your talking about odd disk failures: as I said at the top of the thread, if you're using disk, archive stuff in RARs (or other checksummed archives), test those checksums from time to time, and don't purge old backups the moment you make new ones. Or just use tape and you're fine, at least until it gets hard to find a drive old enough to accept the tape (10+ years).