I'm not a dog-owner but I'll defend them since the majority of people walkings dogs that I see in this area seem to have them well under control and pick up any poo. I did see one guy with a husky-type in Dulwich Park about to leave the poo but I made a point of asking if he was going to clear it up and offered him an old carrier.
He did.
There are irresponsible people who own dogs and don't police their actions. There are irresponsible parents who don't teach their kids any discipline so we end up with teenagers roaming the streets and vandalising public property quite aside from spoiling all those quiet pubs :p.
Perhaps licenses for both dogs and kids? :p