Been wanting to try this, finally did. My jeans gap at the back. I don't care what size I am or they are... I have this problem. They fall down. I don't like wearing belts. I cut small holes on the inside of the waistband. Inserted 1/4 inch elastic, cut about 3/4 the length of where I was putting it.
And this when on.
No gap and they stay up without a belt!!