It's so great to hear all these wonderful stories!
When my mare was back home at my parents, we had a dog. He would always come out with me to feed the horses, so he could get horse treats! He would steal them out of the horses buckets on the ground. The other horse couldn't care less, but my mare would get so mad, and chase him out of the paddock. But as he got older, and couldn't move very fast, she got way less territorial about it. She would still 'chase' him away, but only as fast as he could hobble away.
He would also come with us for trail rides, and always wanted to trot out in front. But he would get tired and slow down, and was getting kind of deaf, so he wouldn't hear us coming up behind him. My mare would always touch him on the back with her nose, as if to say 'hey, just letting you know'. Sometimes it would scare him, because he couldn't hear, but she never stepped on him, even if we were trotting.