Has he been vet checked? 70% rocks in his stool is more than just a puppy eating everything, IMO.
Does he eat other things? Paper, cardboard, etc?
What diet is he on, kibble/raw etc? And how much/day?
This could be a deficiency in a mineral in diet, that the dog is compensating for - or possibly Pica.
What Jax said is correct about the obstructions and the teeth, possibly even a perforated bowel. Either way the behavior has to stop.
How many times are you feeding a day?
Any way you could feed 5 meals a day (his regular amount, just split into 5), so that you could feed him and then take him out for his potty breaks right after? I think it would be worth the effort, just to see if he STILL eats the rocks when he has a full belly.