Halitech is right. glue is meant to hold until you finish by sewing or some type of lacing. Burnishing leather that has just been glued will heat up the glue an make it soft. As far as the strongest glue, it is made( by Mule hide ) and sold at your local ABC roofing supply store, it is called black splice adhesive. once you put the two pieces of leather together they will not come apart