Gosh, I've come over all Tory for a minute - let's see . . .
Dogs are scanned from sensors added to our plethora of urban CCTV cameras - any that are not chipped will be followed by our state-of-the-surveillance-art kit until automatic facial recognition software identified the owner. By the time the scragend gets back to his/her hovel, the local K9 unit from Her Britannic Majesty's Constabulary are waiting with them with two guns - pay the fine there and then and it gets chipped immediately, hesitate and the other one is used for enforced euthanasia. Of the dog, not the owner (I'm not Norman Tebbit after all).
Dog shit - easy. Following the same kit as above, or the DNA profiling as suggested earlier

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, the said excrement is packaged and posted directly through the letterbox of the miscreant for proper disposal. For repeat offenders, see above,
sans chipping gun.
Wow, that was actually quite an experience. My talents are wasted being tolerant all the time . . .