.... what the regulations are in Belize....
Judging from the posts on this old thread, it sounds like others are detecting there. But I'm sure if you ask long enough and hard enough, you can always find a "no".
A humorous (and "telling") example happened with Fisher Co's newsletter periodical in the early 1980s: They used to have a Q&A (letter to the editor) column. And in one edition someone had written in asking "what are the laws re.: Mexico?" (apparently they were getting ready to vacation @ some beach resort down there). Fisher answered back "leave the detector at home, d/t not allowed". In the SUBSEQUENT issue, various other readers wrote in objecting. Saying things like "since when?" and "where did you get that info?" and "we go there all the time w/o issue".
So Fisher, in their defense of the earlier answer, gave more background for their info: They merely asked some border consulate lawyer bureaucrat. Sounds reasonable, eh ? Who better to ask, than Mexico themselves after all eh ? And this lawyer, no doubt, couched their question in terms of raiding the pyramids, or historic monuments, or shipwreck salvor, or exporting gold bars back across the border or ... WHO KNOWS ?
Yet detectors are a common site on Mexican tourist beaches. And all the major manufacturers (including Fisher, doh), have distributors/dealers in the bigger cities.
I know Mexico was not the focus of your question, but just saying .... if you get "dire sounding feedback", sometimes you have to dig deeper to see if it was merely the real-life answer, or someone's "safe" answer to a "pressing question".