If you've ever been involved with teenagers, you'll be aware of how easily influenced they are by appearance. Like it or not, as a teacher, you have to play the part of a "respectable adult" to the hilt if you want to be able to get a class of them to listen to you. :(
As a consequence, I needed to find a way to protect my good work shirts from cheap government-supplied pens, but also in as subtle a manner as possible.
Step 1: The Solution
The were the right size for my pockets, and as a bonus, they were completely invisible inside the shirt.
I place one of these inside the pocket, and make sure to slip the pen into the pocket when I put it inside my shirt.