The Fortified Shield is an item that is only available in The Legend of Zelda: Skyward Sword.
The Fortified Shield is the second and last upgrade to the iron type of shield. It crafted by taking your Reinforced Shield to Gondo, the Scrap Shop owner and paying him 100 Rupees along with the necessary items to upgrade it.
The Fortified Shield is the toughest shield made of iron. Like the other iron type of shield, the Fortified Shield also immune to burning. Unfortunately, it still doesn't protect against electric attacks.