Let me first start off by stating my wife was raised super religious. The kind that makes you feel guilty just thinking about sex. Took some time but I have gotten her past that and things have been getting much more exciting in the bedroom.
Anyway flash forward to a couple years ago when I decided to go for the back door. Nothing to risky, just a finger across the asshole and a little bit of lube. She was pretty embarrassed but went with the flow and as it turned out she enjoyed the new sensation.
As time went on she would be the one begging for ass play. Still wasn't to sure about penetration. She wanted it but was still having feelings of guilt. I found some reading material for her to help ease her mind. So there we are going at it heavy cowgirl, her favorite, and when I put my finger on her hole she grabbed my hand and forced it inside her. Needless to say it was all I could do not to cum immediately!