Hi Ruth
I'm guessing you also have Students as well as staff accessing your Moodle site? Also can you confirm that you don't want the students to be able to view all the courses? Can you let us know what version of Moodle you are running and how many staff users you are talking about - is it 30 or 300?
I would not alter the Authenticated User role as that would provide EVERYONE (including the students) the ability to view all the courses and means you cannot exclude anyone. Others may do this differently but I would create a new role called 'Staff Member' who was allowed to view courses and assign the relevant users to it. Remember that permissions may conflict with a user's other role so you'd need to fully test your set up
Guest access does let people view courses without logging in unless you force everyone to log into the site - this of course depends on how you use Moodle
If you do force everyone to log in then guest access would let any user (who is already logged in) access the courses - including students!
Cheers
Teresa