I occasionally take Mac outside on a harness to explore the backyard. Since I've started doing this, he's stopped trying to get out the front door nearly as much, though stalks me whenever I near the back door. One thing he's serious about is that the back yard is HIS. The nextdoor cat, Leo, is an outside cat by day who goes inside at night. Leo wanders the neighborhood as if he owns it, and likes to roll around in the dirt in our garden. (I don't understand why cats like this, but it may be to cool off.) Once Leo was in the backyard when Chaz opened the back door, and Mac went racing out after him. He and Leo rolled around in a fight, then Leo broke away and dashed over the tall fence to the nextdoor yard, Mac hot behind him. Mac stopped on the top of the fence, though, whether because it was the border he was defending or because of the large yellow lab who lived in the yard, we don't know.
Fast forward to this week. I had come home from picking up lunch, and when I got out of my car Leo was walking down the sidewalk in front of our yard. When I opened the door, Mac met me, as he usually does, and usually I just tell him to get behind the door and he does, while I walk in. Not this time. Mac teleported around me and raced over to Leo. I was halfway through the door, so I put lunch on the couch and went after Mac, fearing the worst. Not my kitty. Mac, who hardly ever goes out the front door, and then only as far as the bushes in front, had raced all the way to the edge of our yard, tale majestically enfluffed. Where he stood in front of Leo, nose to nose, both of them sniffing away. I don't understand this behavior, either.
When I approached, Leo ran off, but Mac stayed right there on the edge of the property. He followed along as Leo left, keeping even with the other cat, and when I picked him up he gave a deep hiss of displeasure. Still, I mentioned "treat" and told him what a good boy he was, so he calmed down and let me bring him inside with no further complaints. I'm very proud of him, protecting our yard but not running out of it. What a smart kitty.