I met a man with ranger duties who patrolled a length of canal towpath which passed through a town - some streets ended at the canal. Spray painting circles around the dog muck achieved two aims - it warned walkers and cyclists where the muck was and it also warned dog walkers that their activities were under surveillance. When asked what he was doing he would say that he was having the muck DNA tested - which resulted in a count of 150 "deposits" on the towpath at the end of one street reducing to one. Bluffing effective in the short term but also indicates some awareness of wrong doing and taking responsibility if pushed.
