You can place a block of wood between the crank and the engine block to stop the rotation, then use a big breaker bar with a pipe on it.
This method has never failed me.
Obviously, the socket and breaker bar have to be up to the task.
A number of sockets haved failed this particular test...
I have personally had no luck with pneumatic tools here, and wonder about the 'beating' that the percussion places on the rod bearings (if they are still in place)...
1986 300E 5-Speed 240k mi.