Unhinged Neighbor -- What To Do

Location: Colorado

We (2 adults and 4 kids) have lived in our house for about 12 years. It is a city lot and houses are close together. During those 12 years, our neighbor complains to us incessantly, about literally everything. Doesn't like cars parking on the city street in front of his house. Doesn't like construction happening across the alley in the back. Doesn't like it if our kids play outside (daytime hours, normal volume). Didn't like it when we had cracks in the walkway between the sidewalk and our house, and didn't like the noise when we got it repaired. And on and on and on. He complains to us and about us on all of these issues, regardless of whether they actually have anything to do with us, and sometimes threatens legal action (he is a retired lawyer).

The thing that he fixates on the most right now is our dogs. We have three dogs who are indoor dogs and only go outside to use the bathroom. They are trained and get a lot of exercise on walks. They will occasionally alert bark at people in the alleyway, but will stop when told to.

The neighbors lose their minds whenever they hear the dogs at all. The dogs are not left outside unattended and we have cameras, so I can say with 100% certainty that they do not bark for more than 30 seconds at a time, and generally give 2-3 barks at the times they have complained. This happens maybe twice a day.

Our city has a mediation program for barking, which we attended at their request. They wanted us to agree that ANY barking from the dogs was unacceptable and that there needed to be quiet hours for our entire family from 7pm until 9am, among some other demands. Of course we did not agree to this, and the mediators did tell them that this was not reasonable. We made a written agreement that they were very unhappy with, since it didn't change anything for us, but did set guidelines about how and when they should complain to us about the dogs.

Since then, they have called Animal Control at least twice that we know of, who told them to pound sand and that they would not be coming out or issuing any citations. They continue to send texts any time the dogs bark once or twice. If they bark one bark at 9am and once at 4pm, they will characterize it as "barking for 7 hours" in the texts. Texting about other issues has gone down a little, but it is still several times a week, and they continue to make threats of legal action.

Is there anything we can reasonably do to stop this? Would this be recognized as harassment? Other than having cameras and documenting everything, do we need to do anything to protect ourselves from legal threats?

ETA that per our mediation agreement, we have to keep a group text chat open so that they can notify us if the dogs are barking continuously for more than three minutes. This has not ever happened, but they continue to use the chat for any time they hear the dogs at all or any other complaints.