

Hi man, if you and your wife just start enjoying anal sex, it needs time for her to get used to it.
Use a lot of lub., fingering her asshole first, need more practice, until she can take two or three fingers without pain, by that time your wife's asshole should be ready for anal sex, it is always better do it slowly and listen to your wife's feeling, don't expect your wife can take it like the girls in porn movies, those girls are well trained and they may use drugs to relax their asshole muscle as well.
Anal sex can be ver enjoyable for woman if do it properly, some woman can have very strong orgasm from anal sex as well, but some woman just don't like it at all, so you need to discuss with your wife but not just satisfy your own desire.
Good luck.