Geocache

[Air Boy]

That's a great point.  I have been looking at different options for the cache and logbook. It would either have to be water-tight and brought up to the surface, or it could be a slate. 

And about the issue of the cache traffic, I think if it was placed in a popular location, such as the pits, word would probably spread.  Even if a diver is not into geocaching, I could see them hearing about it and then getting into it, or looking up the information online.