Do what works best in your own personal situation, secret sharing, leave a riddle that only the specific heir can answer in order to find a location, safety deposit box, etc.

Just be aware that if you are leaving anything significant, people many times act differently when seeing dollar signs. Not just collusion, but refusing to divulge their secret without themselves getting paid.

Either way, you are trusting someone to one degree or another. If the expected passing is decades away, people losing their key material is a significant risk.