It is my understanding, that casual beach beach metal detecting, at the various S. American and Mexican beach resorts, is a common site. I suppose if you asked enough questions, of enough police, bureaucrats, or cruise-ship lawyers (as mackaydon suggests), you might find someone to tell you "no". This would be because, perhaps they're couching the answer in terms of shipwreck salvor type international treasures stuff, or historical monument looting, etc... Yet casual beach goer type stuff ....... well ... sort of like here in the USA: I bet if you inquired about any beach, in any state, under any level of govt. (city, state, county, or federal), and asked with just the right combination of words, phrases, and inferences, that you could also get a "no" here too. Even in places that are routinely detected. So be careful thinking the best way is to ask travel consulates and such. Try this instead: if you are skittish, just inquire ahead to detector dealers in those areas. Most of the major manufacturers (Whites, Garrett, Fisher, etc...) have dealers in other countries, including mexico, etc.... Pick the dealer nearst where you're going, and drop them an email or phone call, to see if their customers go to beaches like those.