On a recent run in my neighbourhood I noticed a sign stuck in the front lawn of a property.
It was a piece of cardboard stuck to a bit of wood. The sign said something along these lines (I didn't stop to read it properly or I wouldn't have been able start running again): "If you walk your dog past here and it poos on my lawn, pick it up."
The house had a high fence with a strip of lawn in front of the footpath.
The occupants would not have been able to see people walking their dogs past and herein lies the problem.
Some dog walkers who think nobody is watching simply don't bother to pick up their dog's droppings.