States generally prevent collection against funds that have been segregated as retirement benefits and maintained in that fashion over time. The theory behind the policy is that the state does not wish for the judgment debtor to be potentially pushed onto the welfare rolls as a ward of the state in favor of a particular judgment creditor or class of creditors.
However, judgment creditors are able to "get at" the pension benefits (assuming they can locate the benefits) once those benefits are paid out to the judgment debtor. Such collections are difficult and cumbersome and time consuming and often unsuccessful.