Is this discussion for police dogs, personal/private use or both?
I like what cliffson1 wrote about training in different places and different circumstances. Our 1st trainer had protection classes. I often wondered if those dogs in the classes would only perform at the facility.
Our 2nd trainer has trained dogs to fiercely bark on command, definitely looks very scary, and a good deterrent. The dogs were on leash so this type of protection work could be done in a variety of situations.
I personally would not want my own dog to be trained to actually bite as part of protection work. I've seen a local K9 officer go through a drill with the ESU and he warned the officers that sometimes K9s might bite an officer in all the excitement of pursuing someone and advised the officers to relax and not over-react if bit. So I would not want to take that chance with my personal dog.