For what its worth, the mrs and I gave up together and the only way we got through was sheer pig-headedness. We gave up at the same time with the agreement that if she started smoking then I could too and every day for the rest of our lives, she would be to blame for every ciggie I smoked. And vice-versa, if I started smoking, then she too could blame me for every ciggie she smoked for the rest of her natural. Now no matter what the pressure, there was no way I was going to be the one who broke. No way was I going to be blamed for her enjoying a fag for the next who knows how many years. She can be as pig headed as me. So that was it. Let no-one tell you otherwise, it's not easy. We ended up have a screaming match over a game of Scrabble, because I had a great word for the top central triple pointer (blazer) and she put at 2 letter word in the way to block me.
I used to deliberately stand near smokers, so I could indulge in a bit of surreptitious secondary smoking. To the extent I once ended up perhaps a little too close to a little old 80+ lady standing in a bus queue. I was on the way home from work and the bus stop was just outside the house. Then the wife walks past and realises instantly what was going on, laughs, the little old lady looks around, and well you can guess the rest.
So, my advice? devise a penalty that is unbreakable and just too awful too contemplate. How about something along the lines of:
If I start smoking again, I will drive the wife and any old flames of her choice to a restaurant, sit outside for the duration, pay for the meal and drive them both (to their respective) homes. That should do it. Oh and you will post on GC to tell everyone you have failed and how well the meal went for them both.
That should do it.