if the govt. wanted to they could require that banks report details of all foreign deposits to the finance department. a few clicks of a mouse could easily trawl records and retrieve this info.
governments worldwide are becoming wise to the ease with which money can be quietly and anonymously moved around the world these days in order to avoid being taxed and the loopholes that facilitate it are rapidly being closed.
buying gold and diamonds, high value and easily carried and sold are a possible workaround.