Stop or My Dog Will Shoot
The Simpsons Season 18 Episode 20 (05/13/07)
Recap
When Homer gets lost in a cornfield maze, Santa's Little Helper rescues him and becomes a local hero, which prompts the Simpson family to enroll him in Police Dog Academy, where he dons a new and more stern personality. Meanwhile, Bart, missing Santa's Little Helper, gets a strangling snake as a new pet.