Lock events (or disable drag and drop) in iCal Drag &amp; Drop in iCal is very convenient, but last time, I accidentally moved an appointment (or at least, I'm not sure, if I did...)

Is it possible to somehow "lock" important appointments?

Or alternatively, to lock all appointments/disable drag and drop?
You can't lock an event, but if you add an Invitee (yourself maybe) then it will prompt you after making any change.