Avoiding user refresh of pages with forms

Is there a way to prevent a re-posting of the form data when a user pushes the "refresh" button on the browser? I have a page that has a form to enter credit's or debit's to a user account. The top of the page displays the users account history and at the bottom is a form to add an adjustment. I just had a situation where a user came in complaining that the database is out of control every time I "REFRESH" the page the credit I put in gets added again and again!! He also claimed he was getting no warning message about that which was of course false, he just didn't read it. In any event, I need to make this more user proof. Thanks, Jeff