In a large saucepan melt lard over moderate heat. Add pork, salt and pepper and simmer until tender. Cook about an hour, being careful not to crisp the meat. Remove pork and set aside until cool. Shred the meat by hand or with tines of a fork. Remove and discard any remaining fat. Transfer to a medium saucepan, add the arbol salsa and cook over moderate heat, stirring frequently. Serve or assemble within a toasted corn tortilla to make taco. Carnitas can stay refrigerated for up to five days before assembling within a taco.