"Sumo protecting Avery from something bad, like dragging her away from a dangerous situation or about to attack someone that hurt Avery."
Avery is a really rambunctious kid, constantly needing to do something energetic or creative, and it's inevitable for her to find herself in stick situations more often than is desired. Strangely, Hank is glad to have a daughter so spontaneous and adventurous, despite his anxieties that follow from his past. Avery keeps him on his toes, and she's ambitious in her great escapades, it teaches him to adopt the same feelings.
But Hank isn't as young as he used to be, and he does still worry, so his partner in crime is always two steps behind to jump into action. Sumo, the bullsterous St Bernard that's loved Avery since she first started peaking through the buttons of Hank's shirts, has been protecting her like no other person could. He watches her like a hawk, ready to pounce if she calls.
When she was a baby first learning to walk, he would stay at her side so she could fall against his warm, fluffy body, rather than the hard wood floor. When she got curious about the dog food in his bowl, he would carefully take the material of her shirt in his mouth and drag her back. When she cries at night because of a loud noise, it was Sumo who would be there before anyone else, and sometimes his heavy pants and wet nose was enough to console her.
Avery's not a baby anymore though, so her dangers are beginning to be real threatening and somewhat scary. While riding her bike on the street, Avery is approached by an older man in his early 30s. Avery isn't naive to "stranger danger" (it's impossible given her closest family are all involved in the protection industry), so when he compliments her bike, she ignores him and begins to ride back toward the house. He's persistent however, following close behind asking what her name is, where she's going, anything to get her to talk. She doesn't speak until she sees Sumo resting on the front lawn, and jumps off her bike running for him.
"SUMO, HELP!" She yells, and in an instant, he jumps up and charges for the older man, barking ferociously. Avery hides promptly behind him, smugly grinning rather than afraid, and laughs as he runs away from the sheer volume of the enormous canine. When he's out of sight, Sumo turns to Avery and nuzzles her close, and she in turn cuddles him lovingly.
"Thanks, buddy. Let's go inside." And with that, she leads him in and cuddles up in front of the television, using him like a pillow.
Avery doesn't need Sumo to know what might harm her, but she's smart enough to know people respect big before they respect small, and if her repayment is lots of belly rubs and throwing his chew toys, she's happy to keep up the bargain.