It would appear that the fine folks at Tiffany are against using metal detectors to find jewelry of the sort... just take a look at how they find it!
http://news.yahoo.com/ex-tiffany-exec-given-prison-2-million-jewelry-191742817--finance.html
http://news.yahoo.com/ex-tiffany-exec-given-prison-2-million-jewelry-191742817--finance.html