See what I did there? Eh? Eh? Magnetic! As in this product from iStik (warning: annoying loud background music) which uses neodymium magnets that let you attach it to workout shirts, jacket pockets, or your backpack.
Of course, neodymium magnets are very strong, and can damage hard disks. It works fine with the iPod nano's flash memory, however. You also might want to avoid wearing the iStik on your shirt front if you have a pacemaker or other cardiac device.
iStik is $25 for the second-generation iPod nano, and $27 for the third-generation "fat" nano. Terrible magnet jokes sold separately.