Trim most of the fat from the meat, leaving a thin layer. Cut into 4-inch pieces.
In a large, heavy saucepan, melt the lard over medium-low heat. When it has melted but is not yet very hot, add the pork, water, orange zest, lime zest, garlic, and salt. Cook at a gentle simmer, stirring occasionally so that the meat evenly cooks, for about 2 hours, or until the meat is tender. If the meat needs more time and all of the water has evaporated, add a bit more water and continue to cook until the meat is tender.
Once the meat is tender, raise the heat to medium-high. (Don't panic if the lard comes to a rolling boil – this will diminish as the water evaporates and will become small bubbles.) After the boiling lard changes to small bubbles, cook the meat for about 25 to 30 minutes, or until light golden brown and crispy all over. Remove the meat with a slotted spoon or tongs and drain on paper towels. Sprinkle with the salt. When the meat has cooled slightly, pull the meat apart using 2 forks into shreds and smaller pieces and discard the bones.
To heat the tortillas, heat a medium skillet over low heat. Place the oil in a small dish and before placing in the pan, brush both sides of each tortilla with 1/2 teaspoon of the oil. Place the oiled tortilla in the skillet and cook until just warm and soft, 2 to 5 seconds per side. Remove from the heat, place on a plate and cover with a cloth to keep warm until ready to serve.
To serve, make the tacos with the meat and warm tortillas, and garnish with the guacamole and pico de gallo.
Yield: 4 to 6 servings (makes 3 1/2 to 4 cups shredded meat)