It is difficult for creditors to garnish an offshore bank account because U.S state courts do not have jurisdiction to issue a writ of garnishment against a foreign bank with no U.S. branches. Keeping cash out of creditors’ reach would not be difficult if all one had to do was open a foreign bank account while making required IRS disclosures.
It is not that easy; it is very difficult for an American to walk into a foreign bank and open a personal checking account.
There is an interesting article in Forbes about difficulty with personal foreign bank accounts. The article explains that there are many legitimate, non-tax reasons why a U.S. citizen would want to hold money or investments in another country. The way to do so is to invest through foreign financial firms with ready access to foreign banks and securities.