Read the fine print very carefully on the prepaid card. In most cases, its a complete rip off. Why not take advantage of a free consultation with a local bankruptcy attorney and explore your options so that you wont' have worry about this creditor every trying to garnish you again?
No attorney client relationship exists unless we have a written contract. Nothing in this post should be interpreted as legal advice.
Technically the money is exempt from being garnished regardless of what type of account it is in. The problem is that if the creditor that holds the judgement against you actually garnishes the funds, you will be in the position of trying to prove that all of the funds were from your pension to get them back and that may be a very hard and time consuming thing to do.