Maybe Groundspeak is not ready for this but here it goes... I am thinking of a moving/travelling geocache. Think of it a bit like Einstein's Theory of Relativity, while the geocache will never have a fixed coordinates (GPS) in the world, relative to the transport object (cruise ship in this example) it does have a fixed position.
So, is this possible? Any suggestions? I was thinking along the lines of a Geocache page in the ship's library book.
A listing guidelines update in spring 2003 ended moving caches. Periodically there are threads asking for them to come back, or proposing the idea afresh, not knowing they used to be allowed for the first 2.5 years of geocaching. In one such thread, I wrote the following summary of the issues leading to the change in policy:
It's highly unlikely that the policy prohibiting moving caches will be revisited.