Can I make an OS X ESD (or other USB drive) read-only? I have a USB Flash drive onto which I've used Disk Utility to restore the Mac OS X Install ESD:



Is there a way I can make the result read-only, in order offer it at lease some semblance of protection from accidental change?

I assume (but don't know for sure) that I cannot make the raw disk itself read-only, so higher levels of protection are okay, but the lower the better.
One thing I have tried is using Sharing &amp; Permissions to set rights to Read only for myself, like so:



This prevents some writes:

megaweapon:Mac OS X Install ESD matt$ touch foo
touch: foo: Permission denied


but if I try to make modifications through the Finder, I'm prompted for my password for administrative access.

Unfortunately, this is not a hard defense against write access.  To accomplish this, a USB stick with a write lock switch (hard to find) or perhaps an SD card in a reader might work.