I tried back stitching like SGT Rock suggests. I used normal weight Wally World poly thread and found that the thread had broken in multiple places after hanging in it overnight - I used black thread, so it was easy to see. I used a pair of tweezers to remove the broken threads and then back stitched with heavy weight Gutterman poly. I decided to use black to see if this also broke. Nope... This was what I needed.
The display in our Jo-Ann's does not have outdoor upholstery thread like SGT Rock suggests, but they did have "heavy weight" in spools with 100 meters of thread.