The amount of dog waste on city sidewalks is out of control! The issue is how do you prevent this or enforce the laws requiring dog owners to clean up after their pets. As a dog owner there have been times that I found myself bag less, however there is always a bag or something else within a 10 foot radius I can find to pick "it" up.
About 10 years ago at a city council meeting a 4th grader proposed "Doggy DNA" where dog owners upon getting their dog licensed would submit DNA samples and the city could then identify the owner of the droppings left behind. Although I thought this was brilliant I understood it wasn't that practical. Perhaps it becomes mandatory dog walkers/owners must have a bag in their possession while out strolling with their dogs. Maybe the parking authority can enforce this while they are out making rounds and a summons can be issued if there is no bag.
Another thought is to have a page on the cities website where people could submit photos of violators. Then comes the issue of the clean up. This is a citywide problem and although the property owner is probably not the culprit here, possession is 9/10 of the law. I would ask that property owners clean up the mess on their sidewalks. The waste left behind by these inconsiderate dog owners gets tracked all over the place and becomes a real quality of life issue in town.