Adair is correct...chances of success starting with a plant that has 2.5 gal root ball are slim to none... it may live, but the roots and stone relationship will never look right! make some cuttings from your plant this year...then start your project next year...or search out some young material to start with this year. Very little has been mentioned about your stone...good stones are harder to come by than good containers...it would be really frustrating to work a project like this for several years only to be later disappointed that the stone you chose sucks! If you decide to give it a try...I strongly suggest starting several...much more likely to get something you are pleased with down the road.
I would never leave one buried in the ground/pot for 10 years...you need to work and expose the roots over time...you also need to insure that the roots are following the contour of the stone. I doubt I would ever let it go more than 2 growing seasons without taking a good look at the progress.
I say all this with limited experience developing root over rock