I realize this is an old thread, but in case anyone is just stumbling on it like I did, I can personally vouch for the fact that it's not all secret. One of our local K9 units trains with the local Schutzhund club regularly (sort-of separate but some stuff jointly, it's neat to watch), and their trainer also regularly works with local K9 SAR teams as a volunteer clinician. The latter isn't quite the same as watching them train, but we're still learning his methods and he talks a lot about training police dogs. Both the local K9 units (county and city) also regularly give demonstrations at public events like the State Fair or animal-related fundraisers (recently I saw them at a big fundraising event for a new facility for the county animal shelter), and actually try to bring a mixture of dogs from ones just starting in their training to experienced K9s.
A random member of the public wouldn't be allowed to sit in on one of their regular training sessions (except the weekend one they do at a public park with the SchH club), but I think that's more about liability and distraction than anything. Having curious onlookers at every training session would get very tiresome I'm sure, so a blanket ban makes sense to me. It's the same reason why they now restrict ride-alongs to people who have a reason--people who want to become LEOs or other first responders and need the experience, volunteers like police chaplains who do it as part of their training so they can understand what the officers are experiencing, that sort of thing. They used to allow anyone with an interest to go, but it became overwhelming and distracting (and thus dangerous) to the officers, so they restricted it to special circumstances.
Some methods they use in training might be bad publicity because training working dogs isn't always pretty, but honestly I think that's a pretty minor concern for my local police. I've actually seen one of their closed sessions and didn't see anything that most people would really have a problem with. I realize that's just one session and as others have said, training methods vary by department, but I'd be surprised if it's a PR
thing for them. In fact, generally APD encourages interest in and questions about their training methods, as part of a strategy to rehabilitate their image (as a department they had many problems with corruption and excessive violence, to the point that the current chief of police was appointed specifically to reform the department, so it may be a bit of an unusual case, I will admit).
My mom is a police chaplain, I give clinics to the mounted police unit occasionally, and I'm a member of a K9 SAR team that works with the police trainer I mentioned, so that's where my knowledge is coming from, just for full disclosure.