More Words, Deeper Hole

Huh. Five minutes before I read your comment, I was reading about the Northern Mariana Islands (because of Trump's electoral win there). Here's an excerpt from wikipedia:

The first European explorer of the area was Portuguese navigator Ferdinand Magellan in 1521. He landed on nearby Guam and claimed the islands for Spain. The Spanish ships were met offshore by the native Chamorros, who delivered refreshments and then helped themselves to a small boat belonging to Magellan's fleet. This led to a cultural clash: in Chamorro tradition there was little private property and taking something one needed, such as a boat for fishing, was not considered stealing. The Spanish did not understand this custom. The Spanish fought the Chamorros until the boat was recovered. Three days after he had been welcomed on his arrival, Magellan fled the archipelago.

Considering the story of the "stolen" boat, and considering your comment, I don't see how the cahes would work out very well. To directly apply the story of the boat, does anything stop visiting aliens from simply absconding with a cache? And if not that,what helps prevent other sorts of misunderstanding or miscommunication about what to do when a cache is found?