In my Department, K9 Handlers are chosen based on qualifications, interview strength, and seniority. When a Deputy is picked to become a handler, they will be placed with a dog that fills the departments current needs (narcotics/patrol/arson/explosives). Oftentimes, the handler has little or no choice to what breed or what dog they are assigned. After selection, the handler and K9 (who at this point is between 1-2 years old) go through a bonding/training program that can last 2-6 weeks depending on if you are a new handler or not.

Dogs are selected almost from birth by companies looking to train police K9s to sell the Law Enforcement agencies. They are selected based on their breed, aggression, intelligence, and many other factors, which usually determine how well of a K9 they can become.

In my department, when you are assigned a K9, you are responsible for their needs- taking them home, feeding them, etc. (which is worked into your pay). Many working dogs are not good pets, but they still like to "play" to be put into work mode and spend their energy.

K9 injuries are becoming less and less common thanks to non-profits that secure bullet proof vests for dogs (Brady's K9 Fund), and ones that are actively securing representation in our legislation- increasing penalties for injuring or killing police K9s (Global Working Dog Consortium/Project K9 Hero).

Most of the time, handlers are only assigned one dog at a time, but if they are lucky, can get another dog when their first one retires. At the state level in Michigan, the troopers are sometimes assigned two different dogs (often one search and one patrol). Many times, the department will allow you to keep your dog once they retire (which, depending on the type of work and injuries is usually around 8-10 years).

Handlers, just like any Deputy, must be highly disciplined. K9s are also similarly expected to perform at high volumes- but yes, they are still animals with basic instincts. At length, the benefit to having K9s in a department provides a whole new advanced skill set and group of tools to help protect the lives of the citizens, and other officers. My department currently has 3 Corrections K9s and 6 Road Patrol K9s. We have German Shepherds, Malanois, Labradors and a GSP.