Preventing users from powering down clients during backups

Hello.

I'm asking because I'm sure I'm not the first to encounter this problem.

A client is powered on, sooner or later Bacula tries a backup and it 
finally starts, however it does not complete because the user powers 
down the machine again.
How did you solve?

Ideally Bacula would be able to postpone shutdown until the job is 
finished, but I think I'm asking to much.
Letting the user know that a backup is running would be better than nothing.

I tried installing tray monitor: I see the black icon and I hoped it 
would animate or change colour when a job was running; alas, it doesn't. 
The users would need to click on it and check and it's asking too much 
on them.

Any idea?
How are you coping with this scenario?

  bye & Thanks
	av.