Try this:
Code:
ctcp 900:deop *:*: {
  .
  .
  rest of the command
  .
  .
}
ctcp *:deop *:*:.notice $nick You cannot deop users with higher access than yours.


If they don't meet/exceed level 900 anyway, they won't get the first ctcp to activate.
The 2nd one would tell them that they can't use that feature.