I killed the old guy at depot A, after a looong time shooting him with my marauder rifle. He eventually ran out of hypos and slowly died. I managed to kill him by doing the open door - shoot- close door tactic with his dogs piled up at the front, preventing the old man from opening the door. Its kind of unfortunate though, he didn't have much of value. He should have something awesome for being the toughest person to beat one-on-one in the game, assuming you don't use my cheap tactics