My wife is fairly vanilla but one day we were on the couch and she was in a summer dress and I was casually fondling her. When I playfully asked if I could continue she shocked the hell out of me by saying "You should probably take what you have been trying to get for a while." and pulled out some packets of Vaseline for me to lube her ass with.

This had taken me about two years to get her to this point. I always use lubes part way during foreplay and frequently will rub her back passage with some and when fingering her will often gently insert one or two fingers back there.

The one thing I always do is if my playing becomes too painful -- I stop.