How do you hide a coin for 400 years?

As part of an upcoming blog post, I’ve been trawling the Internet for information about Elizabethan coins. Mostly for curiosity, as I know very little about old coins. Something I’ve learnt: historical coins are valuable. Five-figure prices aren’t unheard of, and I found one coin selling for nearly £100k:

A Triple Unite from the Oxford mint, a gold coin produced for Charles I in 1642. It was worth sixty shillings.

Which got me thinking: suppose you were an unscrupulous time traveller, and you wanted to make some extra cash. Going back in time, getting some coins, and then “discovering” them in the present day could be quite lucrative. But how do you do it in practice?

You can’t just bring the coins straight to the present. They’d be in much better condition than a coin that actually waited for 400 years, and carbon dating would be thrown off. Your coins would be derided as fakes, or at least prompt some tricky questions. You need to hide them somewhere in the past, and retrieve them in the present.

But where do you leave a seventeenth century coin so it’s still safe in 2018?

It’s certainly possible, if expensive – the Tower of London have been looking after the same jewels for centuries. But I don’t think it’s trivial, at least not without attracting some attention. It’s very tricky if you don’t have outside help. And the further back you go, the harder it becomes – imagine trying to save not coins, but dinosaur bones.

I wrote this as a late night musing, but while sleeping I realised it’s not just a theoretical problem. Nuclear power creates nuclear waste, and that waste has to go somewhere. Most plans involve putting it in a bunker, and sealing the bunker for at least 10,000 years – but how do you stop future humans exploring? How do you ensure nobody opens your radioactive death bunker?

Suggestions on the back of a postcard.