This may be old school but when I was younger I made about 60 new gardens for people,and plowed up many repeat customers gardens year after year.My machine of choice back then was a Gravely rotary plow.That thing would chop up large roots and throw a brick out or large stone.One area close to me is well known for its hard rock filled soil.I am not trying to say it did not have its challenges but that gravely plowed 8 inches deep and made the gardens.
One thing is for sure if you hit something you better hang on.That thing could kick like a mule.For about the last dozen or so years I have used a BCS.They are not cheap but I have only replaced tines once in those years with a normal tune up once in awhile. The BCS is a good tiller,I just walk beside it and let it go.The rocks have been long gone from my gardens,so it is easy to run.