Here's the recipe for an injection used by Chris Lilly from the Big Bob Gibson BBQ Team from Decatur, AL. for pork shoulders.
3/4 cup apple, juice
1/2 cup water
1/2 cup sugar
1/4 cup salt
2 tbsp Worcestershire sauce
Inject shoulder with injection solution (1/2 oz. Per pound).
Coat well with rub mixture (4 oz. Per shoulder).
Gently pat shoulder so rub will adhere.
Treasurer, Great Lakes BBQAssociation
Rubbed, Smoked, and Sauced Competition BBQ Team-
22 1/2" WSM, 2 18 1/2" WSM's, 22 1/2" Weber Kettle