Penny in yo' pants - or not

Most of you probably saw the Penny in yo' pants video that was making the round of the internet last month.
I thought it was cute, but as a pants wearer I didn't really think about it.  BUT Saturday morning I was wearing a nice comfy dress and we decided to go to the grocery store.  I grabbed a penny on my way out of the house and a rubber band off the work bench.  I twisted the rubber band around the penny, but when I got on the bike, the rubber band and penny flew across the driveway.  Thinking that perhaps my leg over method was too vigorous for the penny, I redid the penny and rubber band while straddling the bike. (It has a sloping top tube).  But when I got on the saddle - no dice.   So I rode to the store without a penny and didn't flash anyone.

I've been trying to figure out why it didn't work for me.  The dress is knee length and a stretchy cotton.  But when I (and probably you) sit on a saddle, I'm sitting on the the back of the dress while the front hangs demurely over my knees.  So the front and back don't line up like they do when you are standing.  I don't know.  But it was fun to try!