I've used Barge for years. Nothing that I've found holds better. It's flexible, waterproof, and very very strong. If the glued surface separates it's for one of two reasons: One, one or both of the surfaces to be glued were smooth or slick (which is fine, or can be at least) and the user failed to prepare the surface to be glued properly by abraiding them prior to application, or, two, the material you glued/bonded failed structurally. (ie the material ripped, or otherwise came apart). I've never seen a correctly glued project come apart unless the material failed, and in such a case, you can still see the glue is, ironically, completely intact.
If you need 2 things to stick together forever and have a completely flexible bond, Barge is what you want. Just use it in a ventilated area to avoid beathing Toluene.