MM
Yes you are right. I have tried exactly what you suggest. Let him make a mess of something AND then demonstate what years of experience can do too. (But do get it right!)
It worked. He was walking around with his tail between his legs........for 5 mins!
It then became a pissing contest with him trying to out do me on everything, tea included!
I sometimes wonder if the "smack in the mush" may actually be the only way!!!