One day, he was out walking her, and three guys came up to him. They stood around my friend in the usual threatening triangle formation, so no matter which way he faced someone was behind him. They started accusing him of stealing from them, and started to get aggressive until one noticed his dog and asked if she attacked. Just a moment later, she launched herself at the three of them - only the tight leash saved them from being bitten. She'd die to protect her family.
Whenever I visit him, she "attacks" me - launches herself at me so I can lavish attention on her for as long as possible. If he ever had to get rid of her, I'd take her in a heartbeat, but depriving her of the kids she loves so much would be one of those heartbreaking moments you'd never want to see.
What I wanted to say is that you'll have a much higher probability of success with a race that's known to be aggressive, if that's what you want, then with a race that was bred as a companion dog. And half-breeds can be very aggressive or very friendly, but it's essentially a lottery.
Interesting that you'd say this -- I think there's always exceptions to these rules, and here's mine:
I had a half-laborador, half-pitbull. Like a lab, she was very aware of people's emotions, and like a pit, she was strong, aggressive, and had a very high pain threshold. (She barely reacted when we pulled porcupine spines out of her nose with pliers.) Unfortunately, this was a problematic mix. If I was the least bit uncomfortable with somebody, even if it was just social anxiety and I wasn't in any danger, she would start growling and try to make them go away. And she viewed every other dog as a mortal threat, to which she would react with murderous fury. I have no doubt that if I had felt physically threatened, she would have done serious and possibly disproportionate damage.
I wasn't able to take her out much.