Step 1: Acquire Chunk of Flesh item dropsThe first step is to acquire the
Chunk of Flesh item which is a random drop from zombies when you kill them, approximately 1 out of every 100 times. The fastest and most reliable way to boost for these is to call for an exfil and kill zombies at the exfil point; but obviously do not exfil. This should spawn a lot of enemies increasing your chances for the item. The exfil points will become active again after 60 seconds. You can grab as many of these as you want, but 2 of them is a good place to start.
Step 2: Feed Chunk of Flesh to Doghouse map locationsFind a doghouse on the map. The locations are random and change in every game. The fastest way to find them is to grab a vehicle and drive through many
Points of Interest and watch for them in the mini-map.
With your chunk of flesh, interact with the doghouse, and give the items to the doghouse. The amount you need to give depends on the zone the dog is in. For Tier 1, it will require 1 chunk of flesh. For tier 2; two are required.
Unfortunately, once the dog spawns, it will always be friendly,
but you will not always be allowed to pet it. This seems like it is based off the hellhound's random given name or the amount of enemies in the area when it spawns.
If applicable, the dog will sit in front of you, allowing you and your entire team to interact with it and "pet it", unlocking the achievement.