Other Help Topics :: Sudo problem, it don't ask for password??!

Don't know if this helps, but...

Quote

The sudoers file should always be edited by the visudo command which locks the file and does grammatical checking. It is imperative that sudoers be free of syntax errors since sudo will not run with a syntactically incorrect sudoers file.

Have you tried this:
dsl ALL=PASSWD: ALL
%staff ALL=PASSWD: ALL

Maybe the staff group is being allowed to run sudo without authentication

Here is a sudoer man page with plenty of examples:

http://www.die.net/doc/linux/man/man5/sudoers.5.html

original here.