One of the reasons I got the tractor was to expand my lawn in all directions. I'm surrounded by thick woods and there are many many rocks. I rented a post hole digger remembering what a horror show a two man gas powered job turned out to be when putting in a deck years ago. It literally turned our hands into hamburger hitting rocks. I guessed right, the 3pt post hole digger was virtually worthless in my lawn. The rental place recommended a power-down model with a rock cutting bit, but it needed more HP than I have.
Using a backhoe to move rocks has also been an experience. I too have hit rocks that just barely poke up from the ground but turn out to be the size of volkswagens. I have a new system. I dig out about three feet around the rock in all directions and if I still can't find a lip or budge it I let it be.
I wouldn't know what to do with it even if I could move such a rock. And it would take 500 dollars worth of topsoil to fill the hole!