Place the pork shoulder, fat-side up, on a cutting board. With a sharp knife, score the skin and fat in a cross-hatch pattern, making diagonal cuts about 1 1/2 inches apart and cutting down to the meat so the marinade can penetrate. Transfer the pork to a large re-sealable plastic bag set over a baking dish or bowl.
To a blender, add the garlic, oregano, cilantro, cumin, lime juice, orange juice, chipotle and adobo sauce, 3 tablespoons salt and 1 tablespoon pepper. Drizzle in the olive oil and pulse until you have a nice puree. Pour the marinade all over the pork, being sure to get it into the deep cuts. Zip the bag closed and refrigerate overnight.
Preheat the oven to 350 degrees F.
Add about a 1/2 inch water to a roasting pan fitted with a roasting rack. Remove the pork from the marinade and place in the center of the rack.
Cover with foil and roast until the pork is fork tender and deep brown in color, 4 hours. Check on the pork after 3 1/2 hours; if skin is not deep brown, remove the foil for last 30 minutes. Transfer the pork to cutting board and let rest for 20 minutes before slicing into thick pieces. Spoon any remaining pan juices over the meat to serve.
Recipe courtesy of Guy Fieri