My friend usually deals with War Chieftains by getting close to them while avoiding the Fuel Rod blasts. He waits until the Chieftain uses a melee attack, and then he quickly jumps around the back and assassinates them. War Chieftains are the gold guys carrying a Fuel Rod. Only try this if you know you can pull it off 90% of the time and if you are desperate, because the melee damage done by these guys are horrific and can often kill you in one hit.