I remember sitting on the beach as a kid building sand castles and dogs off a lead with there owners walking nearby letting the dog wee and poo on and near where I was playing!
Even worse was when I was in a playground in a park with the kids my mum looks after and a dog owner let her dog poo in the play gound. When I asked if she was gona pick it up and that it could make kids go blind shes shrugged and replied "I dont have any kids" and walked off
But its important to remeber alot of dog owners are very good dog owners. I personally think there should be set areas in every area for dog walking and others where dogs arent allowed (where children play) or atleast have to be kept on leads (for the benefit of wildlife).