Tralfaz, my large economy size dog, almost never does any business outside the home yard---except when we're passing by the home of a buddy of his.
This other dog, whom I will call Walker to protect his identity (he was last seen wearing the Cone of Shame), lives around the corner from us. When we go by, Tralfaz will automatically water his yard if he has even the smallest amount of urine ready for a PM (private micturation).
Apparently dogs can determine all kinds of things from one another's pee, including gender and health status, and I'm sure they can identify each other by it. So I like to think Tralfaz is leaving a friendly "Howdy-do!" on Walker's lawn at such times. I'm sure Walker returns the favor when we're not around.
I would like to note that Tralfaz is quite thorough and careful when he does this. You might say he has good peemanship.
That's how I imagine it, anyway.
For the record, I have also seen that when I take Tralfaz to the dog park---any dog park, and we've been to a few---he immediately drops a brick on the ground. Seems like everything he ever ate reappears, within a minute of our arrival. I don't think he's sending a friendly message. I think it's a way of making his mark on the world. I AM HERE! I AM SOMEBODY!
I wish I could teach him to tag with spray paint so I wouldn't have to clean it up, though.