Help! With neighbors dog.....

My next door neighbor's dog routinely relieves himself in our yard. She's not the most fantastic about cleaning up after Nico but I'm also not in my yard with a baggie first thing in the am when Abby & George go out.

Our houses are close together (obviously) & when he's tied out his leash reaches our sidewalk & what is turning into my lily border.
Does anyone have any suggestions for keeping Nico out of the border? I just don't want to be digging & hit doo-doo or have them trampled before or once they've established. He's a tiny dog looks like a fox tons of hair can't think of the name. I don't want to put anything down that's going to hurt his paws or anything. I just want his to keep his secretions on the other side of the walk. still my yard but not my flower beds.