Center the ornamental iron fence on top of the block wall. Measure the spacing with a tape measure along the entire length to ensure that it is positioned evenly along the wall.
Drill a 2-inch-deep hole through the mounting holes at the base of the iron fence into the top surface of the block wall using a drill equipped with a 3/16-inch close-tolerance masonry bit.
Drive concrete screws through the mounting holes into the holes you drilled in Step 2 to fasten the fence to the top of the block wall using a screw gun.