It sounds like a pretty rugged fence. What are you trying to keep in/out?
Note* Are you installing a 48 foot log fence or a 48 inch tall fence? Is this an open slat fence or a solid fence that will be more prone to wind damage?
If you are installing a 48 inch tall fence with 30 inches in the ground, I think you should be OK with the 3/4 stone. (TAMPED) But it depends on if you are using the fence as a boundry marker or to keep back elephants.
DH has a great idea with installing a short section of chain, below the suface, to aid in the removal of the post.
What do you plan on replacing this fence with in two years? Is there a way to do the below ground prep work now?