I then used a magnet on the inside. One piece on the top and one on the bottom so that they match up when the card is closed. (Here's a good use for those credit card magnets, calendar magnets, etc. that you get in the mail or as giveaways at fairs and such.)
Now, depending on the strength of your magnet, you can cover them on the inside with another piece of cardstock, or if your magnet is not that strong - like mine - just leave it the way it is.