I had a little for some 2 years who would self harm quite randomly it appeared at first. It broke my heart. I'm not a Dom in any way, I'm a care giver, I try to nurture and protect. If you're asking for advice as to how to try to stop it, I would say that you need to try and find out why you're doing it in the first place. There's little point in trying to suppress the actual harming, I think you need to get to the cause of it. You can physically stop someone from doing something but those feelings will still be there - I think you need to establish what's causing the need for you to do it in the first place. My little felt it was the result of her relationship with her father, which had broken down very early in her life and the cutting was her way of releasing the pain. Having done a lot of research we tried (together) to confront her feelings (largely by talking about them) which wasn't easy for her as she didn't want to revisit those memories. It took time and it took patience and things were never perfect but eventually the self harming occurred less often. But it only happened because she was prepared to release those feelings buried deep inside her.
As for the aftercare, that was actually easier. It involved love and attention and her realisation that her self harming didn't affect what I thought of her. The kind of love and attention you get depends on what type of daddy/caregiver you have. The best ones will know how to make you feel comfortable and loved and, most importantly, secure. And then they will make sure you get that love and make sure you're in a better place. My little needed cuddles and hot chocolate and TV to keep her occupied, so that's what I made sure she got