Peeing when scared...

I have a Shiba Inu that is close to a year and a half old. I have had him since he was a puppy and he was housebroken very quickly. He has learned a few tricks in just a few days and is the smartest dog I have ever had without a doubt. But for some reason he has not seemed to be able to break his habit of peeing when he gets scared. If I catch him chewing on something he knows not to chew on, or doing something he isn't supposed to be doing and scold him for it he gets scared and pees. He is housebroken and has not peed in the house in a year other than when he gets scared. What can I do to help him get over this?? Has anyone else had this problem with their Shiba?