I don't stick one in the ribs either. All the aforementioned signs are better ways to tell. My ribs are done after being cooked 3-3.5 hours at 250 on my hood thermometer, which reads a little -- 25-40d -- cooler than the cooking surface.
Can you leave a probe on the grill, to double-check cooking chamber temp, or does contact with the metal create a higher temp than the air temp?
I usually lay a probe from my wireless thermometer on top of a rack, with the temp hanging off the high end. After a while, this is a better gauge than the thermometer in the hood.
Big homemade smoker on a trailer, Weber grill, firepit