Well lets say that I whined for 21 years - to no avail. But interestingly I've used the EF Forum to stimulate her interest. I took (copy & paste) posts (quotes) from various discussions about anal experiences in the Forum and put them in a letter for my wife to read while I was on a business trip.
The posts were mostly from women who had a negative view of anal - then learned to like - even love it - with the guidance of a loving partner.
Not only has her prostate stimulation technique for me improved, but she has begun to allow me to use my fingers with her - presumably with idea of working toward anal sex at some time in the future.
I can't say I recommend waiting 21 years - but at the same time, you have to find a way to get her to agree to experiment with you - even then it's a slow process - but I'm ecstatic to finally get the process started.