The original bag had the cord running through eyelets. Doing that meant a whole new trip to the fabric store so I went with ribbon instead. This turned out to be a blessing as the cord runs much more smoothly through the ribbon. I used a large washer raided from my husband's workshed to hold the bag closed. A washer is easy for 2 year old fingers to manage.
Overall, it has been quite a hit and very convenient. I don't think we have lost a single car since!