Carol you've done nothing wrong here, and you don't owe anyone an explanation.
I sometimes see a dog owner (not all dog owners), letting their dog poop without cleaning it up. It's just a fact of life that some people are like this. However, I would in no way seek to harass anyone in this way, because people (including lone WOMEN, driver) could very easily get the wrong impression. Unless of course, the accusation regarding the dog pooping wasn't the real reason this person was following you. See what I'm saying, folks?
How long was this person following you, Carol? Always carry a phone and look for potential witnesses. Carry a personal alarm. Tell the person to go away. If they continue tell them you have their registration and will call the police. Then try and find a populated area. If they continue scream for help and let the personal alarm go off.
Dog pooping is one thing. Harassing lone women is another matter entirely. If this person wants to continue their issues then they should contact the council, not follow people around.
This driver followed me whilst I was walking my dogs beeping his horn at me and accusing me of not picking up after my dogs. Despite my showing him the two full poo bags I was carrying and telling him that what he saw was my dog having a wee he continued to shout at me through his car window. I am meticulous about picking up after my dogs and he was rude and should learn to mind his own busines.
Was it a small red Mercedes car, Carol? Because the check for this vehicle has issued the following results:
. MOT: Expired: 21 Oct 2014
. Car Tax: No data available
. Insurance: Apparently non-existent.