When Parents Lose Their Cool When Enforcing a Rule

As hard as we may try every parent is guilty of loosing their cool with their child at least once during correction. Now I'm not talking about going over board on a spanking here, rather when we as parents fall prey to our child's natural talent to turn the tables on us.
For example, you discover your child has been emailing a friend you disapprove of and have told your child they can't email them. You approach your child calmly and confront their behavior. Ideally you will give your child their consequence and go on your merry way, but that is rarely the case!
Instead, your child begins telling you that you never trust them. You don't have faith in them to make good choices. Or that you won't let them show you how mature they are.
Okay, stop right there! Every parent, when hearing these words from their child is caught off guard right? I mean, that wasn't the point at all and now we have to defend ourselves because we are right and they are wrong.
But what if that is exactly what the child is after? I mean, what if your child has simply developed a way to minimize their responsibility in the situation while you the parent spend the rest of the conversation defending your position.
This is the cool I am talking about and it's exactly what I did again today! Boy I have to tell you it is the hardest thing to keep from doing, especially when your child knows exactly what makes your guilt kick in.
So parents, how do you prepare yourself to keep your cool even when your kid turns the tables on you? Please share your ideas.
