The best belly band that I've found for those boys who hate belly bands or wiggle their way out of one is this BB sold at Dog.com
Mark Out Wraps Blue - Dog.com
It's nothing fancy - it's like an ace bandage that wraps around the belly several times with nice wide velcro at one end. It's inexpensive (about 6 bucks for an xs) it's not bulky and I've never had a boy wiggle out of this band.