Heat a dutch oven or other heavy bottomed oven-ready lidded pan over medium high heat with just enough vegetable oil (or lard if you have it) to cover the bottom .
Cut pork into 1-2" cubes, trimming large sections of fat off (we need fat for the flavor, so just cut off any real large pieces). Toss pork pieces with spice rub.
When all the meat is browned, deglaze the pan's bottom with the orange juice, stirring to break up the brown bits. Introduce all of the meat back to the pan and cover with water until it's nearly submerged.
Bring to a simmer, cover, and place in the oven.
Stir the pot after one and two hours, the pork should be very tender towards the third hour. When you're confortable with the tenderness, evacuate all the pork to a platter and begin to boil the braising liquid on the stove top.
After letting the pork cool for a few minutes work through with your hands to separate and discard any fat or gristle pieces that hadn't melted in the braise. Tear the meat into smaller pieces.
Serve! We like it best in tacos, but there's no wrong way to eat carnitas.
Carnitas saves in the fridge very nicely, we like to hold back an amount from the last step (broiling) just for the fridge. Later in the week we heat it up, broil and the result is indistinguishable from same-day carnitas.