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well, I guess I confused it with the sea masons... or maybe not.
Added after 13 minutes
we
were
looking for
the treasures of
Caribbean
aborigines
with a metal detector
"Seeker"
I came up with the name myself because I couldn't find a metal detector that starts with the letter "I". But I did see the "Excalibur" metal detector, and it seems to be designed for underwater use. Excalibur was also kept in a lake for a while, or maybe it ended up there later.