I'd laugh if it wasn't such a cool idea. Now you can play hide and seek in one of the most high-tech ways possible. Garmin, the maker of great GPS systems now makes what they call the Chirp. It is a little unit that you can store information on, and place in chosen spots for others to find, and discover your message, talk about online, and track using GPS.
All you have to do is buy garmin chirp and get in on the game. The Chirp performs many functions, including letting you know how many people have found it, coming within the selected range. The unit lasts for up to a year in the place where you put it, until you have to replace the battery. I can think of so many ways to use this, and have fun with it next year on the boat. Since almost every boater has a GPS at their helm, it will get lots of hits if I hide it along the river where we cruise.