Mix all rub ingredients together. This will make a big batch of rub that you can use now and later.
Pat venison shoulder dry with cloth or paper towels. Rub it liberally with olive oil, then rub. Wrap it with plastic wrap, and refrigerate 12 to 24 hours.
Place venison shoulder in a lightly greased heavy-duty baking pan. Add onion, carrots and celery to the pan.
Place the uncovered baking pan in a preheated 375-degree oven, and roast until evenly browned on both sides, about 30 minutes per side. Add about 1 inch of liquid (beer, wine, stock) to the pan. Cover tightly with a lid or heavy-duty foil, and lower the temperature to 325 degrees. Depending on the size of the shoulder, the next step can take up to 6 to 8 hours.
After a couple of hours, check the pan and add liquid if needed. Check again in another 2 hours then every hour after until the meat starts to pull away from the bone easily. It's not done until the bone can be easily removed. When it is done the bone will pull cleanly away from the meat.
Allow meat to cool, and enjoy now as you would any pot roast, or collect and cool chunks of meat for refrigerator or freezer storage. Meat can also be used for tacos, enchiladas, quick soups or laced with a spirited barbecue sauce and piled high in a bun for a great sandwich.