Can I make an OS X ESD (or other USB drive) read-only?
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.