Braylen Harlamert, left, pets Celina's K9, Nick, as Jack Ebbing looks on from the background. Nick and his handler, Dan Harting, recently visited the preschool at St. Paul's United Methodist Church.

The Celina police officer gets out of the cruiser gingerly and stretches leisurely before snapping to attention at the sound of his partner's voice. Nick, the department's K9 unit, does not move as fast as he once did, but his n . . .