The maximum width between picks in a wrought iron or ornamental iron fence that encloses your pool is 100mm (that is 4 inches), additionally a fence built from conductive materials needs to be 1.2 (5') from an exterior swimming pool[exemptions can apply if it is tied into the grounding system of the pool] with no more than 100mm gap beneath the fence. From the inspectors perspective, they should not be able to fit a 4 inch sphere through the fence.