I would love to have anal sex with my wife. How should I broach the subject?

I know she enjoys it when I rim her asshole and when I push a finger in, but she does squirm a bit if my finger stays longer than 30 seconds or so.

Can one of you wonderful ladies give me step-by-step instructions?

__________________
"Even a man who is pure of heart
And says his prayers by night
Can become a wolf when the wolfbane blooms
And the moon is full and bright."