The concept is generally wide open. They do not want "cartoon like" images. They prefer strong images. The concept of a dog house is okay, but not the primary vision. Maybe showing two dogs and one being a lab, with another looking more police dog like. Not needed, but an option.If you do a version with a dog house, then it should be bold. Subtle imagery of a police badge in there somewhere could work. If using a shadow of a dog, I would suggest more of the protection type. 
Suggested colors, Navy, White, Orange. They are open to any colors as well.

The Dog House Academy