To prepare pernil puertorriqueno, begin at least 24 hours in advance with an 8- to 10-pound pork shoulder with the fat on. Crush six large cloves of garlic, and mix with 1/2 teaspoon black pepper, 1 tablespoon dried oregano and 1 teaspoon of salt for every pound of meat.
Add 2 tablespoons of olive oil and 2 tablespoons of white wine vinegar to the garlic mixture, and place in a blender. Mix well.
Next, wash the pork; rub it with the juice of 2 large lemons, and pat dry. Make several 1-inch-deep slits on all surfaces of the meat, and then coat the meat with the seasoned garlic, making sure that the paste penetrates the slits. Cover the roast with plastic wrap and refrigerate for 24 hours.
To cook the roast, preheat the oven to 300 F. Place the meat in a 2-inch-deep roasting pan with the fat side up. Cook for about 35 minutes per pound, or about 4 hours for an 8-pound roast. Do not cover the meat with foil, and do not turn. If the skin is not crispy by the time the meat is done, turn the heat up to 400 F for about 15 minutes, watching carefully so it doesn't burn. Let the meat sit for about 30 minutes, and then remove the skin. Carve the meat, and cut the skin into slices. Serve each slice of meat with a piece of skin.