gorilla glue as u said is a urethane glue, but is only good for glueing shoes rubber and other plastics that are non-porus. The way white, yellow and hide glue works is the glue is dissolved in a solvent (water), and the polymers get sucked into the crevases cracks and pores of the material being glued as the solvent evaporates. urethane glue works on the same principle, but the solvent is acetone, and it evaporates a hell of a lot faster, and that doesnt give the molecules enough time to be sucked in the material. Also triming the excess away from the glue shouldnt make a difference, as the excess isnt attaching the surface.
my 2c,
luke
edit: Doc i beg to differ you can separate a g glue joint, if you apply acetone to the glue joint... well soak the joint in it, it will come apart fairly easily.