Has anyone had rubber bands to wear after getting their braces off?

I just got my braces taken off (finally-- yay!) and they left on two of the back brackets for me to put a rubber band across the front of all my top teeth for two hrs a day. I'm doing it, but I've just never heard of anyone else doing this. Has anyone else?

And, if so, do you have any ideas about how I can keep it from riding up and resting against my gums? It is supposed to rest across the front of my teeth (which are bracket free now) and it keeps slipping.

Note: I have a permanent retainer on both my top and bottom teeth, if that makes any difference...

Thanks :-)