Put all ingredients in stock pot and simmer until fork tender (easily comes apart when fork is pulled through). This can take up to 4 hours, but start checking around 2 hours.
When done, remove meat from pot to shred. Two long-tined forks work well for this. Shred all the meat, then return to liquid and reduce slightly- cooking over medium heat 10 minutes or so.
Not only is this cooked meat delicious in burritos, tacos and over rice, but it freezes well for use later. If you have leftovers, be sure to pour any liquid from the pot in with the meat for storage- this will keep your leftovers flavorful and moist.
To adapt for a slow cooker, use ~1 qt water and 5 tsp bullion. Cook on low 6-8 hours, then follow directions as above, turning slow cooker to high and heating shredded meat in cooking liquids 20 minutes or so (to reduce).