Custom Document Properties

Hello All,
I managed to create and update custom properties for a word doc in VB. When I open the doc afterwords I can see these custom properties in the custom tab of the properties window. (Click File-> properties in word 2000+ or OfficeButton->Prepare->Properties and the select Advanced properties in word 2007).
I want to add a custom property in VB but not have it be changed when openning the doc. It can be visible in the doc or not - that does not matter what matters is that it can not be changed within the doc.