My pen drive is very important to me. I have a 32GB one, with Ubuntu 12.04 on it. On then pen drive, I created two partitions; one ext4 for Ubuntu (5GB) and the other partition is fat32, so that windows can access it too, with restrictions.
Windows users without my permission can't see nor modify anything in my fat32 partition. However, when I boot from my pen drive and log in with guest account, I can see the fat32 partition and do whatever with it, delete it if i want.
I just want to restrict access to that particular pen drive (only for the guest account). I also don't want to disable the guest account, because if somebody boots from my pen drive and just want to check mail or save an image from the Internet to their own pen drive, they need to be able to see/mount their pen drive.