I would rent a decent size dozer with teeth on the bottom of the blade that rips up anything to about 6" below the surface & have it done in no time. Or build an attachment like it for your bobcat. The problem is you may never use it again.
' below the surface & have it done in no time
"I walk slowly, but I never walk backward." - Abraham Lincoln
"If we ever forget that we are one nation under God, then we will be a nation gone under". Ronald Reagan
"Patriotism is supporting your country all the time, and your government when it deserves it". Mark Twain