Several Observations.

The center is concrete, that would need to be cut with a diamond or carbide disk.

Getting to the back side to cut it with an oxy-acetylene torch would be difficult. Would you reach through and aim it back at itself?

If you ran a piece or two of 1" rebar down the center of the concrete that would make it even more secure.

If you used some of that ultra high strength cement like used in the Berlin Wall that would be even better.