"Damn it!"

You heard me, he said "Damn it!". I thought I was hearing things the first time it was said, so like an idiot I said to my child "excuse me what did you say?". Clear as the first time he said it he says it again for my benefit. "Damn it". Yikes! Ok I am the parent what do I do now???? I have read all of THOSE articles in the magazines and I can not remember what any of them said! How on gods green earth do I correct that? Deep breath I stop. Think for a brief moment. Then say "hey bud who says that?" That is my investigative work. He says "I dunno". Clearly not the answer I was looking for. You see in our house we do not swear. People who come to our house do not swear and if something squeaks out we do politely remind them that there is a child in the house. So I continue. "Do you know where you heard that?" He says "no". Ok 0 for 2 I am loosing the battle. So in my best mommyrox voice the best thing that I could come up with is "well, bud we don't say that. When we get frustrated we say Oh Sugar!" (FYI, That is one of my favorites) He looks at me and says "OK". I have lost this battle to a 4 year old and I may loose the next one, but the war, my friends is not over. When I get home I am going to search out all of those old parent books and scour each and everyone until I can find the one that tells me how to effectively correct this kind of behavior. Now, you may ask why not search the internet you big dummy? Good question, duhhh gotta go. Looking it up now.