Interesting. If I did that I think I would lose my desire for a sessions. I like to "fast" before a session. But, I hear you about calling a safeword because you don't want to cum.

You could also consider seeing a domme who doesn't care if you cum or not. A Domme I saw in Germany a few years ago found it funny that I was about to cum 15 mins into a 2 hour session. She was SOOOO good. So she just decided to force it and once it happened told me that it doesn't change the fact that she gets to play with me for another 1 hour and 45 mins. She just kept going with the session and I came 2 more times before it was over. She was trying to get a 4th out of me but I had to beg her to stop it was just painful at that point and I thought the skin on my dick was going to peel off.

What's crazy is that I had a super hot date later that night and we went to the Kit Kat Club. But, I didn't try anything sexual because I knew I was spent... at least for the next few days.