If this is a real problem you have, and not just a thought experiment, I think rather than burying the data on some unreliable medium, your best bet is to just pay someone to store it for you offshore, away from the dictatorship you mentioned.

There are plenty of consumer-grade cloud storage services. I’m sure there are more niche ones specifically for long-term archival as well, which would usually be cheaper per bit, per-year, if you don’t need to access the data regularly.