Says it all really. I just witnessed a neighbour's large dog do a huge shit in the middle of our front lawn. He did come over to pick it up, but I suspect that was only because I had seen his dog do it. I commented that it wasn't really acceptable to let his dog wander all over our lawn. He replied, "what's your problem - I'm clearing it up aren't I?" He never has the dog on a lead, and I said that if he allows his dog to wander all over people's gardens then it ought to be on a lead. His response was that he didn't think it needed to be on a lead. I didn't agree 
I think common courtesy really would be that you don't let your dog walk all over neighbours' gardens, you keep it on a lead until you get to the nearby dog walking field, and if it does have an accident then you pick it up and if you are seen by the home owner then a quick "sorry" doesn't hurt, does it?
Btw it isn't just our lawn he lets his dog shit on - there's at least two other front gardens the dog gets directed onto.