Hi All,
First of all we as HR should have a great rapport with all HODs and employees also, we should be in a position to get the information that the employee is uncomfortable with his job, should initiate the discussion with the employee and as well as the HOD, there is no wrong in sharing the information with the HOD because all the information what you get may not be right but alerting the people is not at all wrong.
I agree it is very difficult to get the information but it is not difficult. As a HR guy you should be prepared with successors and have an eye on the guy who is planning to leave.
There are occassions where we have arrested the issue even the employee is scheduled to attend the interview, this can be possible with your rapport, each one of the employee will surely have one or two close friends and without discussing with them they even forward their resumes also hence if your efforts are high it's not a herculous task.
Tea points, smoking zones, gettogether places, lunch rooms, library, parking slots, in the common company transport etc., are the right places to obtain the information.
Thanks and regards - kameswarao