police dog 
noun
A dog, especially an Alsatian, trained for use in police work.Three police dogs are in training with the county's constabulary to wear new lightweight head harnesses fitted with small cameras....
- He is one of only a few GMP-bred puppies judged unsuitable to become trained police dogs and are instead re-housed in good homes across the region.
- We could send in some of our specially trained police dogs who may be able to tackle someone in this situation.