Looking for help with an unusual money question.

First some general info:

I'm creating a treasure hunt and the prize is a large sum of money - 6 figures.

I don't want to hide actual cash because it may be some time before it is discovered, and cash may mold/rot etc. People are still looking for D.B Coopers stolen cash, good luck with that...

To further complicate things I will be the only person knowing the whereabouts of the treasures location, and I may die before it is discovered, so IOU's are not an option.

My question is, how can I positively convey this "treasure" to the finder using a method I am not aware of? Also, I don't want to burden the finder with having to sell valuable items such as gold etc. Most answers would probably be that which is why I am mentioning it.

I have some ideas but don't want to taint others answers.

Maybe a Banker or Financial Advisor could be helpful.

Thanks for any help offered.