Preventing a resource from being written

Hi,

Suppose that I want to prevent a resource from being modified, just read. And I use only what Webdav or ACL offers, not DeltaV.
What can I do ?
I can't set a infinite lock on that resource : it's "dangerous" and not nice ;o)
I could use the access control protocol, maybe, but I don't know how to proceed : must I create juste one principal, that represent anyone, and has a "read-only" right ?
What would be a good solution ?

thanx