I've known many people who have tendered resignation letters and are then immediately ostracized by the company, security follows them around everywhere, they're asked to leave the building immediately, etc....
Don't do that. If this person wanted to cause damage, he would do so without announcing his resignation. Take some precautions, but don't treat him like an outsider. He's still an employee during his notice period; treat him like one.
Remember, he's leaving somewhere where he spent a good 1/3rd of his life. Change is not easy, and paranoid asshole-ish behavior makes it 100x as hard. Plus, you want him to be an ally to your company in the future, and not a potential enemy.