Touch screen protectors are always a pain, it's just a question of how much pain
I used to use (overhead) transparencies, with one or two corners cut to slightly larger dimensions then the screen, so i can tuck it under the screen frame. Used to have one a tablet, and long time ago on an iPaq 3670. It held on pretty tightly (thanks to the oversized corner, static electricity and partial vacuum under it) and worked on both, the iPaq and the tablet, so i guess it works just fine on both passive and active touch screens (as long as it's not too thick).
Most transparencies i tried fared against scratches somewhat better than most dedicated screen protectors, but once they got scratched, it was more visible, so you had to change them every now and then.