When I was a teen working in a welding shop we used to assemble magnets in a framework about half the size of a brick that would exert about 750#'s of pull on a steel table. They were really simple once you understood what you were doing. 4 fairly weak rectangular ceramic magnets aligned so they were repelling each other wherever they interact at all would create a much more powerful magnetic field. Not just flipping one magnet over so it repels but also rotating it 180 degrees.