I (of course) fully agree that solid nerve is absolutely a must in the kinds of protection/security/police dogs we're used to dealing with and talking about. My aim is to (experimentally) breed different lines of 'bull-herder', for different roles- and one of those lines would be like an old rough, rustic rustic farm dog (think dogo sardo, cao de fila de sao miguel etc.). Those dogs traditionally have high defense/low threshold- but not always the absolutely most solid nerve, when really pressed.