Although I have never walked my two dogs in the park described, I know exactly what the writer means.
I daily see people walking their dogs on and off leash, so I think enforcing a “dogs on lead only” rule in that particular park would have no effect) while the owners are either on the phone, chatting to their companion or purposely looking the other way while their dog does its business.
I count myself and the friends I walk with as responsible dog owners. While always picking up my own dog’s mess, as do my friends, I make it a rule always to pick up two others, especially if the mess is on a path or track where it will be trodden on.
As with all other undesirable dog problems, the owners must be blamed for creating this problem.
It only takes a minute to pick up and it is the right thing to do.
So come on you lazy dog owners, you are giving all dog owners a bad name that we don’t deserve.