After several months of dating, katie came fully into the relationship eight years ago, and Peter and I collared her.
katie had some some bad relationships in the past, including ones with other Dominants (although pretty shitty ones, in my opinion). Due to those relationships, she believed that her worth was focused on her vagina, and getting fucked. (I won't go into the details, but let's just say that if any of us ever meet the guy who was katie's Dominant before she joined us, I don't think it'll be pretty.)
When we were dating there were a lot of discussions about what katie needed and wanted out of the relationship, and it was decided that after she was collared, she would be anal only. For eight years, katie hasn't been penetrated vaginally at all, taking both Peter's cock and my strap-on up her ass and in her mouth.
I've watched over the past eight years as katie has bloomed into someone who understands the pleasure an anal only life can bring. she learned to orgasm anally, and is allowed to cum freely, but only if she is being anally penetrated at the time.
From a selfish side, having a submissive who is anal only has been nothing but a positive. Taking the focus away from her 'normal' pleasure zones has allowed her to feel arousal much more acutely, and there's nothing better than a horny, desperate sub eating you out because you've told her that she's not going to be fucked and allowed to cum until she's made you cum a few times by servicing you orally

I think that all of us agreeing that katie was going to be anal only was the best decision we could have made for our relationship, and I'm looking forward to many more years to come.