Between the tension and friction, the belt itself doesn't move. It holds your shirt down and your pants up.

I wear the straps to keep my shirt down and the belt to keep my pants from shifting.

I've used the Flex Belt as well as shirt stays. I prefer the shirt stays. I found these on Amazon...search for: World's Best Shirt Stays from Shirt Stay Plus BLACK 4-PIECE. I'm sure these are the brand I have.

I've used them for the past 4 seasons and have had good luck with them. It is true that they tend to disappear over time. I originally bought a set of 4 and I think I'm down to 2 but I will buy them again. I think the price was about $12 for a set of 4.

They are adjustable. They have metal alligator type clips that attach to the bottom of your shirt and top of your hose/socks. The hose I currently use come up above the knee so its important to be able to shorten the length and these do the trick. (I'd post a photo but I don't know how to imbed them in posts)

Shirt Stays
 

Here's a cheaper version of the neattucks.

http://www.amazon.com/dp/B017LXZNZU?psc=1

KG

+1. NeatTucks are the best.