Reauthorise user before saving / updating

I need to prompt user for there password before changing critical information on a form.

I am use DevExpress ASP.NET Data view in model edit form mode.

I added a Password property on my Business Object which is NOT loaded from database and acts pretty much as a write only field.  This password is sent to database on update for validation in my update stored proc.

How do I create a business rule that requires this field to be present if any properties change?  Would using the IsDirty property in the evaluation of the business rule help?

Kind Regards

Tim