Oh jeez, I guess this was a topic I always knew would come up eventually...
So, police dogs. Honestly a very, VERY controversial topic - both in terms of police ethics and in terms of animal husbandry ethics. Sticking to the actual dogs, the way police dogs are trained, whether they're strictly a search dog or a bite dog, has been proven to make "civilian" dogs avoid them. This is bc they're trained to sit at attention unless off-duty, and dogs interpret "at attention" as "ready to square tf up". So when the dog retires, and they still follow their training bc they're a dog and don't have a concept of retirement, they struggle when it comes to socializing with other dogs. They pretty much have to be kept away from "civilian" dogs a majority of the time.
And that's if they even get to retire. A lot of police K9s die on the job, because they're the one being sent directly at the danger. Other times, a attack police dog is deemed too dangerous due to their training, and their "retirement" is being put down when they get too old to work anymore.
Still, there are police K9s who get to become house pets. But they can only be owned by either a police officer trained to work with K9s, or a police K9 trainer. Because again, dogs don't have a concept of retirement. They also don't understand the context of what they're being trained to do. They just want to do the job because it makes their humans happy. But for these dogs, that means they can never be a normal dog ever again.