Protect/Unprotect as an event??

It seems like it ought to be simple....

I have one sheet with one (ActiveX) checkbox.
I want to disable the checkbox (gray out) when the sheet is (manually, not programmatically) protected, and enable the checkbox when the sheet is unprotected.

It would seem that, if there were such events as Worksheet_Protect and Worksheet_Unprotect, this would be the solution. No such luck, as far as I can tell.

HELP!