Well, I find that when that feeling comes -- and it comes stronger for some women than others -- you just cant clench off. I mean, of course that is the normal reaction. It is what we were taught all our lives. But if you have a partner you love and trust, if you push out just a bit, rather than clenching off, the entire act goes smoother. Why? When you clench, the hold is this shape -- * -- hard to penetrate anyway. So you clench more, he pushes more, it is like you are fighting against each other. When you push, even slightly, the shape becomes an O. And what is easier to penetrate -- * or O? Yes, it takes some time and practice to be at ease with this. But once you can control that 'gotta poop' feeling and allow him deep thrusts, that feeling changes to one that can help you orgasm. Anal is a mix of voluntary and involuntary movement inside. Both can help you orgasm if you relax, breathe, push and have a partner you can communicate with. It is also good to practice on your own to master this feeling. Once you do, you actually look forward to it, rather than dread it. Good luck!