Talk to them face to face for sure, they may not even know that their dog is doing it, or may not know it is actually harming your plants
we have a HOA facebook page and its comical at times
Everyone gets on there and gripes about their neighbors online but they never tell the neighbors in person
My neighbor always complains about the neighbors to the side of him parking his work truck on the grass, but he will not say anything to them in person which would likely clear it all up.