Leave Denegar's Stand by taking the road heading southwest. Follow the road up the mountain to the entrance to the Iron Fortress. Head inside the fortress where you will find Iron Fortress Defenders, Iron Fortress Deathblades, Iron Fortress Dragoons, and Iron Fortress Deadshots wandering the entire complex. The Deathhowl Mastiffs can be found in the courtyard of the fortress. Kill your quota of walking dead and demon hounds before returning to Donald Saref for your reward.