The Nano does not come with much included in the box (just a dock adapter, USB cable and headphones), so you may need to invest in a protective case, armband, or other accessories -- these quickly add up and Apple knows it.
Users also had a problem with the security of the armband - some felt the iPod did not fit snugly enough in the band, with some users reporting that their iPods fell out and broke.
Because your guests may want to wander in and out of the gated area, you'll need to have some type of armband or stamp system if you want to maintain crowd control.
The nano armband serves to the let you strap your iPod in place and go, giving you access to the control wheel but keeping your hands free for all that exercising.
You can get lucky on St. Patrick's Day - or any day - as a slightly naughty leprechaun in a green vest with matching hat, bow tie, suspenders and armband.