are you talking about just a single piece of leather? or stiched pieces? if the pieces are stiched together, and such as a belt they get stretched, and stretch differently, cause them to seperate, and one to start to fold over.
If it is just a single piece of leather, then i agree with above that it is too thing for the application. When I make belts I try to use a ten to twelve weight leather to make sure that it isnt going stretch. If you are a big guy, or put big stuff (such as large revolvers) on your belts, a cheap walmart belt isnt going to do the job. This is where you need a good hard thick leather, if the leather you have seems "spongy" to the touch it is going to stretch out.