Can you block saving a work item with a rule of some sort

I would like to prevent saving a work item with type 'defect' if the user has changed it's state to resolved-fixed and there is either
* a comment with a specific format missing or
* an attachment suffixed with patch missing

Sometimes we forget to attach the patch for the fix or specify a few obligatory comments (usually input with a template, so the structure is common).
If we could get a reminder when we slip, we'd save ourselves a lot of pain.

Is that possible at all? (If so, how)

/Morten