That's a toughie. I am sure you're already familiar with uoa.org and all the other websites? The only thing I know that can protect your skin is grease. But if you apply vaseline you'll have trouble getting the bag to stick. The only thing I can think of is creating a contraption that has a 1 way valve; So any contents that go into the bag can't come back at you. Have you googled this topic? There might be some athlete out there who has already figured this out. Is there any chance your gastroenterologist is a cyclist/athlete? Maybe your surgeon (they're all so macho you've got a good chance there). Perhaps you'll end up inventing the perfect solution, getting a patent, and getting rich!! Or at least help others along the way. Good luck. Of course let us know if you do figure out a solution.