Ya know...since moving the furniture around in the house my cat LOVES to sit under my computer station. Only problem is that when I 'share' the space with him he claws and bites my feet!!
Keep a can of compressed air near by. It is very effective cat repellent when needed. You only need make the noise and not blow it at them. I suggest not blowing it when your guy is under the desk as they usually pop 3 feet straight up. If you choose to do it while he is under the desk have a video camera near by.




