Make a notepad document that contains a random number sequence, name it something unassuming like j.txt or hurr.txt then stash your files in a .rar archive that is secured with a password that is the random number sequence in the notepad document, then take the hard drive and lock it in a safety deposit box, then take the safety deposit box out of the bank and burn the bank down to try to make it look like your stuff was lost, then bury the box in rural Kentucky and promise a poor family $10 a day to guard it, then shoot them all in their sleep and throw the box in the challenger deep in the Marianas trench, let Cthulu guard it for all eternity.
Simple.