How is a metal detector different than any other electronic device that people would routinely have with them ? Eg.: laptop computer, medical device, musical instrument, smart phone, etc... And question for you: How did you arrive at the information that they would "confiscate" it? And only let you have it when you get to the beach ?
I'll bet you dollars to donuts that you found out about this by inquiring ahead of time: "Hi. Can I bring my metal detector?". Right ? Then I'll bet that persons boarding those cruises, in decades past,
did the same thing. And hence are the reason for this odd rule. The "pressing question" gets passed back and forth between cruise-line lawyers and engineers. Someone decides it will interfere with navigation equipment ? (EVEN THOUGH YOU'D NEVER EVEN TURN IT ON). But gee.... are you/we glad we asked ?
Actually, there's been threads of another cruise line that says "no" to both bringing it, and/or using it. And I'll bet you dollars to donuts here's why: Same as above: Well meaning persons asked. The question gets posed to border consulates. Who couch the question in terms of shipwreck salvor laws, raiding the pyramids, and exporting gold bars. Never mind that metal detectors are not illegal there, and are a common site on the beaches. The cruise-line must answer the 'pressing question' with the "safe answer". It's as if we md'rs can be our own worst enemy.
that merely means you didn't ask the right persons there, with the right combination of words/phrasing. Whatever cruise line you *think* is ok with it, I bet I can fetch a "no". I would just call or email them with the question. With references to "dig", "holes", "take", "remove", "cultural heritage", "interfere with navigation", "indian bones", etc.... Then I would be sure to put a contract in front of them to sign, allowing me (after all, they love to sign notarized contracts). And I bet I can get a "no" from any cruise-line you think is ok.