What is enough to prevent city defections?

[BiggN]

If you don't want a city to switch sides on you... build a Wonder in it...

I've never had a City switch sides that has a wonder built in it.

[Blaupanzer]

It's defininitely NOT culture, despite what the military advisor says when it happens. I had a Zulu city defect to me, pre-1AD. In 1550, it went back. Over half the citizenry was mine by then, th place was producing 21 culture per turn on its own, and my overall culture is at least twice theirs. I had five units (one was artillery) in the city, with population of 12. Some clue as to what causes this either way would be useful. Incidentally the Zulu did not have Espionage, so the city was not subverted.

[Elias Haviola]

The subject line should say it all. I'm starting to get greatly annoyed by the defections. I'd like to hear about what you, through experience, think is a large enough amount of military units in different situations to prevent defections. One unit per population? Two? Does the ADM or health of the units matter?

Do you think there's a unit amount that will guarantee the city not to defect?

I think it's not good that Firaxis has not disclosed the formula for defections or corruption. Strategy gaming should not IMHO contain intuitive elements in this sense. The probability of any event should be calculable, after which it's up to the player to choose to take the risk or not, like for example in the case of combat. Otherwise performance becomes less dependant on skill and more dependant on luck.