In all seriousness, I would make him a decorative shield to hang in his office and buy something like this for non-combat protection:
Ceramic plates are designed and proven to be bullet stoppers. I appreciate your attempt to build him something cool but a defensive situation is the worst time to discover that your gear isn’t up to the task. When he’s in the field, he’ll wear his issued body armor and any extraneous gear will not be allowed by his superiors.
You could always get one of the shield blanks Nathan suggested and somehow affix 20 or 30 (or 40) layers of ballistic kevlar to the back of it if you’re really serious about bullet resistance. Kevlar basically functions on the same principle as the ancient Greek linothoraxae, and that many layers of Kevlar 29 (Style 745) should be enough to stop most of your more common handgun rounds, at least. Especially after going through the aluminum slows it down a bit.
That being said, though… I’m also going to agree with the above posters who said that trying to use a shield to stop actual bullets fired by a hostile enemy is a bad idea. Especially a round one. But if you’re just wanting to make him something as a lark that has a chance of stopping a round or two in a one-in-a-million office shooting scenario… I’m not going to stop you.
But taking something like that into a hot combat zone? In the words of the noted 21st century philosopher Will Smith, “Aw hell naw!”