Rub garlic, seasoning salt, pepper and cayenne pepper to taste onto roast.
Place roast in a large Dutch oven and fill half way with water; add onion. Bring to a rolling boil over high heat. Reduce heat simmer and let cook until meat falls off the bone. This should take at least 3 to 4 hours depending on the size of the roast.
Place hot roast in a serving bowl and pour on your favorite barbecue sauce. Stir until well blended. Serve on your favorite buns.