In that case, I would insist on the pelvic floor therapy and talk to his doctor about a sacral implant.
Does you dad take any med like Lomotil or Imodium or does he use psyllium husk to bulk the stool?
Also watching the diet to balance insoluble and soluble fibers. After my surgery, I started with a very restricted diet, totally low fiber, and started adding one new food a week, or the same food differently (from cooked to raw, or from peeled to not peeled), so I could find out what would provoke gases, diarrhea or constipation. It can be helpful to consult with a clinical dietitian or nutriologist.