Time Machine + WD My Book

I bought the above combo last week for my new iMac. It sort of works ...

The problem I have is when I leave the iMac and it goes into sleep, then on wake the WD My Book is "disconnected" - so if I don't remember to go to the Time Machine and see there have been no updates, then the Time Machine isn't backing up. Once I spot it, then I have to go to the WD software and manually reset it.]

Any ideas - my concern is that it isn't very automatic, and that I will losr data if I don't remember to go and check when I wake the machine.

Thanks
Stephen

You mention "the WD software". Did you install the WD Backup application on your iMac? If so, first thing you need to do is uninstall that crap.
If you leave T.M. on, it will backup every hour. If your iMac goes to sleep, T.M. will stop. When you wake your iMac, T.M. will resume backups based on the next hourly scheduled backup. So if your iMac was last backed up at 3pm, went to sleep at 3:30pm, woke up at 6:30pm, T.M. won't backup again until 7:00pm. Unless you go into T.M. preferences and tell it to backup now.