Correcting the leaky gut means correcting the intestinal imbalance of micro-organisms and systemic candida. You can't repair leaky gut with fungal candida present causing ongoing damage to the intestinal wall. He'll need to revert the fungal candida back to its yeast form, correct the pH, boost the immune system, restore normal tissue flora, etc.
Some of the beneficial bacteria that gets destroyed by antibiotics can cause constipation. That bacteria is also responsible for producing fatty acids(butyrate) that protect the lining of the small intestinal.