I am a new CO owner, and my Yogi is only 7 months old, so I am no expert.  In my research of CO's, prior to buying Yogi, I was told to expect 2 periods of "fear" in his puppy year. One at 4-5 months, and one at 7-8 months. 

I have seen some of that recently, but the first episode was a cat cat that literally "attacked" him, running from behind a garbage can, stutter stepping on his head and hissing as he charged Yogi would have scared any puppy.  He is now wary of other dogs, and will get "defensive" when the "cat mafia" appears on our walks, but he doesn't really show fear. 

When someone comes to the door, he is naturally curious, and will bark, and go to the door, but when told to "hush" and "sit", he backs away and waits until he can sniff/approve. By the same token though, he apparently "sensed" something "off" about the cable contractor, and he wouldn't let him in the house, where the postman and the pizza delivery guy are fine and kind of disregarded...so long as they don't get near me.

When he is behind the fence, he does not have the prey drive to attack squirrels, birds, people, cats, etc.   He will notice them, and alert to them, but he doesn't run from them, or get "insane" trying to get to them either.  He has, from 10 weeks old, placed himself between me and whatever is in the yard or someone approaching me. You don't get near me without that tail going up, those shoulders getting set, and those feet stomping to go with this guttural, bear like growl.  He does not bark incessantly, nor does he charge the gate if it is left open.  He "guards" his yard and definitely protects me but even on walks or in the truck, he is kind of cool and laid back, "relaxed", alert but he isn't on the "attack" immediately...except with my husband. 

Yogi does not see Josh as "pack leader", he sees him as "playmate".  He is more "aggressive" in play with him, and a kiss from my husband will have Yogi pulling on his clothes, and nipping at his arms, jumping on him.  I see this is "bad" but Josh has completely disregarded any training I have applied, and kind of pays the price now. he

Now is this training or instinct? I've socialized him, taught him basic commands, reassured him to new people, places, things on walks but he isn't some highly trained dog. I attribute it to his instinct, he knows what is dangerous an what he can disregard.  What I do not know is how he will react if someone tests him - like if a dog came too near, or if (like the cable man) he decided that person was a threat. If someone came into his fence without being let in.  He is definitely protective and I feel he would absolutely act aggressively.

Which is exactly why I bought him.