Rule number two: If you think you have found a no expection rule, you haven't gone through the examples yet.
Rule number three: The exceptions of the rules are the most important cases.
Runle number four: Whenever you try to use the exception rule, you find a case where the rule works and vice-versa.
Oh, I was just kidding. I have never heard about these four rules. It would be interesting to know them. Right now I am trying go check whether the rule that says that only nouns/pronouns can follow a prepositon has an excpetion.