We need to bring our sites down for some maintenance, and need to make
it so that any URL to a page on our site redirects to a single page we
have with the "site down" message.
How can I do this?

I tried setting the DocumentRoot variable in httpd.conf to a directory
with the message as an index.html...and of course that works when
someone just goes to the basic domain name...but not if someone tries
a URL that takes then directly to a different page. They just get
requested URL not found on server error.

If someone can just tell me what part of the httpd.conf to look into
to do this, I can research it from there.
Thanks!
-Liam