Yes, obviously that's the first thing to do. I plan on bringing it up next time I see them. They're a little difficult to catch. It's hard to know exactly how to approach it, since I know that they KNOW their dog is pooping in our yard (our houses are so close together, and I see their footprints in the snow where they stand and wait for their dog), so I know it's not an oversight, but rather a blatant disregard for courtesy.

I hope I get a chance to bring it up with them without having to make a visit just for this purpose (which seems a little more harsh, for some reason.)