Hah, that's totally something I've seen before. My last neighbor's beagle decided my tomato plants were its favorite spot. Every afternoon like clockwork, it would trot over and do its business. I got so used to it that I almost missed it when they moved away. Have you thought about leaving a note or just letting it slide?
Hey, that bit about the tomato plants being a favorite spot rings a bell (my cilantro got the same treatment once). But dog waste can actually mess up edible plants, so letting it slide might not be the best move. @taylor.kelly said they're too soft to say anything, which I get, but a nice note usually works better than resentful tomatoes later. Most people don't realize their dog is causing a issue until someone tells them. It keeps the peace and saves your garden, you know?
My last place had a similar issue with a labrador next door. I never bothered to say anything because it didn't seem like a big deal. After a while, I even looked forward to seeing the dog each day. It became a weird little part of my routine. Kind of pathetic when I think about it now. If it bothers you, leave a note, but I'm too soft for that.