I used a stainless steel chain to encode my 24 words master seed. Since a 24 word seed requires 24*11 = 264 bits, the chain must have 264 links. My chain is approximately 12 feet long (3.7 meters). Each link is either pinched/twisted (binary 1) or normal (binary 0). The decoding requires going through all the links, every 11 links (11 bits) you get a word. It's a PITA to decode but it's a cold wallet, so I don't expect to do it very often. I don't even bother to remember the start link nor which type of link is a binary 1 or 0 since there are at most 4 ways to decode the chain (two directions and for each direction two different interpretation of the link).
A test recovery on a HW is mandatory before declaring the chain a proper cold wallet 🙂
The chain can be buried or hidden somewhere, it's not that big. It is waterproof, fireproof and do not oxidize.
What do you think? does it make any sense? How would you mark the links? (pinching, denting, twisting, welding the link somehow, etc…)
Here my chain wallet, yes, it's just a picture of a chain (yet to be encoded!!!)