When I used Hollister appliances, I would wear a belt...it felt more secure. I don't feel the need now that I've switched to Coloplast.
I generally tend to wear short bicycle type shorts (lycra) during the day if I'm wearing a dress or skirt, and at night, switch to cotton men's trunks with my nightshirt. It seems to hold the bag more firmly in place than the belt.
Kismet