A few things pop to mind, depending on what you need.
If you almost never need to change the script, you could burn to a CD or DVD. If you change them every now and then, you could probably get away with a rewritable disc.
You could also use an SD card. Most SD cards have a "lock" switch on the side. When activated (IIRC) it prohibits anything from writing to it, but it can still be read.
Also, you could have a separate partition on your hard drive, and mount it as read-only.
However, even if you did manage to erase the script, you could always restore from your backup
But seriously, if the scripts are important, it would be very
unwise to have only one copy of them.
Hope this helps!