Protect site in Dead Town was a mission in Jak II. According to Torn, scouts have reported Metal Heads moving towards the sacred site in Dead Town. Due to the importance of this location to the Shadow, Jak had to go out there and protect the site from the Metal Heads, for which he was given the Vulcan Barrel by Torn.
Back at Dead Town, there's a lot of Metal Heads around, mostly stingers and grunts but also the new sling blaster and rapid gunner enemies. Sling blasters are dangerous long ranged enemies with a good amount of health. Weapon of choice is the Vulcan Barrel (from now on called Vulcan Fury) here.
Fight the couple of stingers and grunts here and climb the new scaffolding. At the other side here on a muddy spot is your first sling blaster, so be careful to avoid its attacks. There's two more sling blasters up ahead; proceed with caution since a large group of stingers will ambush you if you get too close to them.
Climb up the ruins and you'll be able to see the rapid gunner up ahead, as well as a couple of stingers. Use the nearby pillars to avoid the gunner's range and 'rapid fire' until it has to reload, which is a safe time to pop out and shoot it with the Blaster. Take care to note it doesn't actually move otherwise. When you approach the next room, a bunch of grunts show up; lure them back as another rapid gunner is stationed around the corner.
Nearly there with yet another rapid gunner in the next corridor, followed by a large number of grunts, then a large number of sling blasters and on the final path (a dead end) the last two enemies: two sling blasters. Take these all out and just approach the dead end to end this mission (you can then jump back down the ledge where you just came from and walk back to Haven City.