The phrase "no fear" means,Definitely,will do,don't you worry about that mate(Australian slang?? maybe).
"Definitely Not" I can't really explain this properly but I think i have it right(in my mind, at least).
Heelp.
Yeah. You see I thought "No Fear" was slang for "Definitely" which is why I was questioning using "No Fear" for "Definitely Not" in the first place....Hey Ho