Use cron to schedule a repeating rake task. If you're using heroku, you can get cron as an add-on. But first, of course, you need to write the rake task -- for tips:
http://railscasts.com/episodes/66-custom-rake-tasks/
http://jasonseifer.com/2010/04/06/rake-tutorial
Long and the short - rake is a file that allows you to define various tasks and establish dependencies among those tasks. It's perfect for administrative/cleanup tools, or, in your case, something outside the actual execution of your application.
