Some Local Authorities are very proactive regarding both litter and dog fouling whilst others don't seem to spend any effort. One I have worked for positioned a hidden camera near a McDonalds and have many successes with both fixed penalty notices and prosecutions. Some of the recordings are very entertaining, showing the perpetrators checking around very carefully before they deposit the litter. Similar success has been achieved with regards to dog fouling. They are fortunate in that the staff concerned are keen and hardworking and back up the councils policy well.
One possible answer is, pester your Local Authorities, complain, complain and complain!!