I have an 89 year old widower with a Vizsla, and often dog sits his sons German shorthair pointer and a lady's Vizsla mix. I don't think he knew that his sons dog and the ladys dog was at times pooping in my front yard, but I sure did not want this to continue so I had a talk with him about it. His son would play ball in the front with his dog and actually see his dog poop in my yard and not do a thing about it. When I saw this I went directly to him and ask that he not let his dog poop in my yard, and if he can't control his dog then at least clean it up. I'm pretty upfront, but it stopped the pooping.
If your neighbor (regardless of how old and nice they are) actually "lets" their dog poop in your yard, and they "see" it, then you must let them know it is not acceptable. If they get upset just because you won't let their dog poop in your yard, then your not losing a true friend. Just always remember, honesty is the best policy!
