What is the proper etiquette protocol for ending a session due to a clients aggressiveness?
I had a gentleman whom I told beforehand that I only engage in gentle, soft play. I am not a fan of biting, rough grabbing of the breasts, etc. Despite my wishes, he did so 3 times until I told him I could no longer finish the session.  
Was I right for this? I also returned majority of his donation.

I realize this can be hard if you are actually scared you might offend him, and the violence gets worse, but that's why so many women insist on personal information. This rarely happens when their name and work info. can be put on front street. I have never had this happen, but always have someone who can call you in the middle of a date in case things are getting out of hand. If it's a public hotel, odds are he is not going to make a scene, so asking him to leave should not be a problem. Once, twice, three times? Fk that. If he is on a screening site like P411, you also need to make Gina aware of his bs so they can note his profile and possibly delist him. I would also go one step further and alert him.

you should not have had to return the donation. However, given the nature of the transgression it was probably prudent to do so. I hope you will use the PO board or other means to alert your peers.

Hopefully other ladies can maybe shed light on ways to end things when it becomes rough, but it is well within your rights to end the session.

you should NOT have returned ANY of his donation.  Of course you were in a precarious situation, alone with an ASSHOLE.  But he knew better.......even if he did not admit it in his words or actions.

I can ONLY function under soft and gentle and when a client grabs me roughly and starts to TRY and throw me around, my gut instinct is to hurt him. I take a deep breathe and ask him not to do that and hope he has the sense to stop before I actually come unglued. It has never happened that a guy has continued. I guess my level of physicality protects me in some way. I feel so scared and bad for small women who have to deal with this type of john.

A lot of hookers will not tell you details. They merely mention they have seen the guy and he was okay.  

I have to say that it's not that much different then when a guy gets ripped off and the lady has a 6'8" 300 lb "manager" Sure you want to stand your ground, but is the money really worth getting killed for?

After you told him to "STOP" after the first time (I assume you did that), and he didn't stop, you should have told him right then and there that the session is over and he's to leave immediately.  And you shouldn't have refunded any of his donation--you don't want to reward behavior like that.

Sometimes people say "NO" or "STOP" with such little authority, you can't even hear/understand what they are saying.

To be honest, I really don't know how much information is relayed when checking out references.  I have no problems with any of the ladies I've seen giving out detailed information about our time together to another.  

Personal info isn't going to stop a sociopath.
 
I'm not sure  how personal info would have helped in this situation?

Does it still count as not being able to hear when you cover your ears and go "lalalallalalala"?

It's a communication issue, if someone mumbles, or does not articulate their words clearly. There is a chance that they won't be heard.

THREE times, he was told to stop. I would have just kicked the fker in the nuts and reached for my.... end of discussion.

Absolutely you were right in doing that.
I have always liked SS&E my self. Translation -- SLOW, SOFT and Easy

Yeah a 40l cal. Would send the right message.

He was clearly in the wrong, and you were not only within your limits to end the session, but completely justified in doing so.  

First you was right to throw him out. I would have done so after the second time. It is your body, anyone not following your rules deserve to be thrown out on there rear. In my opinion repeatedly pushing boundaries after being told "NO!" is showing complete disrepect and is a sign of potential real physical danger from him. You was right in throwing him out. Boundary pushing is a small step from far worse offenses like rape.

However should the situation have gotten violent she has a place to start with the police if she went that route.  

The other day a gal told me not to touch her pussy, usually I just get the look that says that. Followed by I already said stop. I was taken back, like... when day she say that? Then I remeber her saying something garbled, and thought to myself of I heard you the first time, there wouldn't have been a second time.

And I sincerely hope she gets selective hearing when you stay stop

She wasn't pissed off, I immediately apologized and explained what happened.

His obnoxious arse would have been bounced down the concrete staircase.  
In this situation, i think you probably did the best you could for the situation to not become any uglier than it was.