Hiro Nakamura, on Heroes, can "bend time and space". This means, briefly, that he can teleport to any location instantly, as well as travel through time, or alter the flow of time as he experiences it. It also means that Hiro Nakamura is the ultimate thief.
The game is as follows: You have some item, a jewel, let's say, which you want to keep out of Hiro's sticky fingers. Figure out some way to store it such that Hiro can't get to it. Because Hiro cares deeply about the space-time continuum, you may assume that Hiro is a well-behaved time traveler, and won't travel to the past in such a way that would create paradoxes (for instance, stealing the jewel before or while you do whatever you do with it would create a paradox). Beyond that, however, anything is fair game for him.
To win, all you have to do is come up with a way to keep the jewel out of Hiro's hands. I'll play the part of Hiro, and respond in the comments to this post. My post for, let's say, Wednesday, will be my solution; that gives me plenty of time to come up with one, I hope. Best of luck!
(Side note: Kiriska complained about my updates appearing at noon, so I moved the schedule up a little for this one. ^_^)
EDIT: Thanks to Æther, I am amending the problem somewhat: The jewel needs to remain intact, and retain its current form, and not end up in another dimension or anything weird like that. :/