Place the pork shoulder on a clean surface fat cap down, score the top of the meat in a crisis cross pattern about ½ inch deep.
Coat the entire pork butt with mustard on all sides then season generously with dry rub making sure to get the seasoning into all the grooves you cut.
Build your fire using a dual-zone cooking method so that all of your coals are on one side preferably in baskets to keep the coals in place. Your target temperature should be between 275-300 degrees F.
You can place a pan below the grill grates and fill it halfway up with water. this will catch drippings from the pork keeping your grill clean as well as adding moisture to the pit.
once the grill has reached temperature place the pork butt fat side down opposite the fire source. Cook for about 90 minutes before you begin brushing with your mop solution. Continue to brush the pork butt once an hour until the pork reaches an internal temperature of 165-170 degrees F.
At this point Its time to place the pork into a 9x13 pan and cover with foil. Place the pork back on the grill and continue cooking until the pork reaches an internal temperature of 205 degrees F. The true test for doneness is to probe the meat with a thermometer. it should go into the meat with almost no resistance.
Once the pork is fully cooked vent the pan and let it rest for 1 hour before shredding. You can hold the pork for up to 4 hours by placing the pork into a dry cooler and covering it with a towel.