The biggest grins we get out of our male (3 years old now, unaltered) is when our 9 year grandson comes over. That dogs bares his teeth, beats his tail, and literally cries when Robert shows up. Robert was 6 when we got Jake and used to sleep with him in his crate, LOL. Jake is a big boy, but he's a sweet, sensitive dog who likes everybody and gets along with everyone, including strange dogs encountered at the park. We haven't had to test his protective side yet, thank goodness, but I suspect he would defend us in an impressive way if it were necessary.
Our female has, from the minute we got her, been protective. Before we were able to establish that we (the people in the family) were higher up than her she would fight us for her food, toys, bones, etc. That's no longer a problem, but she still won't allow anyone else to get near her stuff or ours. She doesn't go looking for trouble, but if it comes to her, she's ready. I guess that's the difference between aggressive and protective behavior. At obedience class, if I leave her on a stay by my chair (where my coat, purse, and gear bag are sitting) she will sit there calmly, but if someone else's dog gets within 3 feet of her, the teeth come out. She doesn't go after them, she just warns them to keep away. She's guarding.
One thing I really noticed with our chessies, they remember everything. We haven't done any obedience work since last November. Went to class on Tuesday and she worked perfectly.
It only works for horse people, LOL, but the analogy of the Arabian vs. the Quarter Horse is a very good one.