flyguy784, I just did a google search on "key Largo" + "metal detecting" + "legal". And I found multiple posts, from various md'ing forums, of people who detect there. How can that be ? So why must a person grovel ? Know anyone (links?) who got a "$500 fine" there ?
As for ecosystem and not bothering sea turtles or dune vegetation: There are scores of beaches in the USA (heck, probably all of them) that have their share of nature-police and dire-sounding "don't disturb the sandcrabs" verbiage. This does not automatically necessarily equate to "no md'ing" and "must grovel" though.