The key to enjoyable anal sex is to use plenty of anal lubricant (such as Maximus) and to take it slowly.
My wife was initially doubtful but willing to try so we started our anal play by using small non-intimidating toys.
After finding out that her orgasms were much more intense when she used a small vibrating butt plug during foreplay or intercourse she was happy to move on to more toys and then full anal penetration. Anal sex is now a regular part of our lives.
We have developed a routine which works well for us.
We start by using a lubricant syringe to fully lubricate her anal passage then we fit a small vibrating butt plug. After a nice session of foreplay she lies on her back with her hips raised on a wedge cushion to give a better angle for anal penetration. We always start with vaginal intercourse though and she often uses a clitoral vibrator so that she has at least one orgasm.
When she is relaxed and ready I lubricate my penis then remove the butt plug and slowly enter her anus. I move very slowly allowing her anal passage to adjust to each movement before going further. When I am in completely I begin to move very slowly then, when she is comfortable, I increase the pace gradually. Occasionall, in a long session, we may add a little more lubricant. She loves to use the vibrator during anal sex and often comes two or three more times before I finish. We prefer this face to face position as it allows me to see if she is in pain or discomfort and also allows her easy access with the vibrator.
I find that my orgasms are longer and more intense during anal sex due, I imagine, to the tightness acting in the same way as a cock ring or similar.
Poop is not a problem for us and, possibly due to the amount of lubricant we use, it very rarely appears. If it bothers you then you could use an anal douche before you begin.