Several years ago I posted about repairing massive separations in my approach shoes using Locktite PL S-30, a Home Depot caulking product with great adhesion and flexibility. I wire brushed it, over-filled it with the polyurethane, and removed the excess with a grinder. Much abuse later, it's hanging in there. I credit the higher flexibility better moving with the shoe than the traditional Barge Cement.
A few months ago I decided to repair the rand on my favorite rock shoes, which had start flapping years before but had become extensive over time. A little more complicated this time, involving masking tape and wax paper, but so far so good. Trust me, I've treated them badly.
Other polyurethane adhesives, available at Home Depot well worth consideration are 3M 5200 (white, less flexible) and Locktite Marine (white or black, slightly stronger than PL S-30/40).
Pretty amazing stuff. I'm finishing an article testing strength of about 20 marine caulks and an article on repairing canvas and sails without sewing. This stuff can be amazing repairing canvas, particularity if sandwiched between layers.