When the pockets or belt loops rip away from jeans I make two small patches, cut from an old pair of jeans. I put one on the inside and one under the pocket or belt loop. I zigzag the patches to the jeans at the same time and then sew the pocket or belt loop back down.
I try to match the patch to the shade of the jeans and I buy denim thread to make the patches blend in as much as possible. It sure extends the life of the jeans.
I experimented with a new pair of jeans this week. I made a small patch and put it inside where the pocket is attached and just sewed around it with a straight stitch. That will give extra reinforcement for the pocket. I hope it keeps the pocket from ripping.