We have an animal trail in the very back end of our pasture. You can see it, it's an acutal path. It's where the wild critters cut across our property to get to the neighbor's pond. We have seen coyotes cut across.
Every time I take the dogs out for a run, both my male dogs will wait till they get to that trail, sniff around and poop on the trail. It is as if they are leaving a message for the yotes that they know the yotes have been by, but this property belongs to them.
I'm curious if your dog is doing something simular. If you always stick to a schedule, then you have a guest, the 'norm' is changed. Your dog is saying, "I know you are here and want you to remember I am here too. I'm watching you."
Hondo Von Dopplet L Bauernhof "Hondo"- GSD
Lilie's Tug McGraw "Tug" - Golden Retriever
Maggie - Mini Dachshund (Rescue)
Lonestar Pivo - Texas Blue Lacy
Ashe - Barn Cat
Katie / APHA