This instructable is pretty self explanatory. For those of you not wanting to spend $5 plus shipping, then waiting for your bit belt to arrive can make this simple hack for your Disney World Magic Bands.
Although I've never had an issue with my Magic Band coming undone, here's an almost free hack to keep it from happening.
Step 1: Supplies
All you need is a small rubber band. This is one of those little ones they sell in the hair dep. in the stores, for doing up little girl's hair. They're less than $3 for a whole bag of about 100 of them, they come in many colors or you can buy just black ones. They also sell them at the Dollar Tree if you have one by your house.
Step 2: How To
Just wrap your rubber band around your Magic Band a little ways ABOVE where your going to clip it on.
About 3 times or so will work, it just need to be snug.
Snap your Magic Band on
Roll your rubber band down over where the two ends come together
Simple yet effective!