I have found that being very clear about when discussion is allowed and when a decision is already made and discussion is closed helps.
I'm a big fan of the "tell me why you think that will work" sort of conversation BEFORE I make a decision. But I get very cranky if debate is pressed on me after I've made the decision. My usual response: "I heard you. You had your chance to make your case. The decision has been made and discussion time is over." If he were to keep talking, there would be consequences.
My little lawyer is generally quite good at letting it go once he has been heard, even if I decide against him because he knows that if his argument is a good one, I will sometimes decide his way. I think that's rewarding logical thought and civil discourse, and I'm okay with that.
But I don't decide first and then discuss. Not ever! That's problematic!
