Tightly wrap the aluminum foil so that the meat is totally encased and nothing can escape.
Now, cover the pan tightly with aluminum foil. Don't skimp!!! You want to keep all that heat inside.
I have never over-cooked one. I have had a Boston butt big enough that I had to cook it for over 12 hours to get it done. The water in the bottom of the pan will not go away if it is wrapped properly and you slow cook. The juice that results make one heck of a gravy. I like to pour a little over my chopped meat and re-wrap it to keep it moist until serving time.
This platter was reserved to top some baked sweet potatoes the next day.