Interesting topic! One dear to my own heart.

As has already been said, trust is most important. If you can't trust your sub to be honest about her actions and reactions, both positive and negative, then you may as well not even bother. But when the trust is there it can be very enjoyable for the both of you.

One particularly effective punishment which I used on an online sub involved forcing her to do something which she enjoyed, but in a manner which she did NOT enjoy. This particular sub confessed to me, early in our relationship, that she frequently masturbated while reading BDSM stories. Being the sweet kind Dom that I am, I allowed her to continue masturbating, as long as she didn't cum. Needless to say, she had a hard time compling with this requirement.

After several unsuccessful attempts to control her orgasms, I thought of this gem. She was to begin early Saturday morning, and she was REQUIRED to have at least one orgasm every hour until midnight. However, she was only allowed to masturbate with her toothbrush.

By noon time, after her 4th or 5th orgasm, she was sending me messages begging to be allowed to stop. About 3PM I received a message that she had found blood on the toothbrush and had stopped for the day. (This was a standing rule with us: no blood, no permanent damage.)

She was unable to wear panties for the next day or two, and had no desire to masturbate for at least a week! An effective punishment to my way of thinking.