Just make sure that their constitution bans legal tender laws and fiat currencies.  Use Panama as an example.  This is what's been in their constitution since the formation of Panama over a century ago:

"There will be no forced fiat paper currency in the Republic. Thus, any individual can reject any note that he may deem untrustworthy."

See this article on how stable Panama's financial system has been vs. even the U.S:

http://mises.org/daily/2533

EDIT: It would also help to ban any form of capital controls as well.