This applescript script will automatically unmount any mounted volume or disk that is not listed as a protected disk.

unmount_disks.applescript

set counter to 0
set ejectedDisks to ""
set pad to ""
-- this should be a list of the disks you do not want automatically unmounted
set protectedDisks to {"Macintosh HD", "Another Disk you do not want unmounted"}
tell application "Finder"
	set mountedDisks to list disks
end tell
repeat with currentDisk in mountedDisks
	if currentDisk is not in protectedDisks then
		set counter to counter + 1
		set ejectedDisks to ejectedDisks & pad & currentDisk
		set pad to ", "
		tell application "Finder"
			-- test this first
			-- when satisfied, remove the -- in front of eject
			--      add -- in front of display dialog
			display dialog currentDisk
			--eject currentDisk
		end tell
	end if
end repeat

-- if you don't want a system notification, add -- in front of the lines below
if counter = 1 then
	set plural to ""
else
	set plural to "s"
end if

display notification time string of (current date) & "
" & ejectedDisks ¬
	with title ((counter) as string) & " Disk" & plural & " Ejected"