How implement security with the mvcSiteMapProvider?

How implement security with the mvcSiteMapProvider?

I need to implement Role security with my mvcSiteMapProvider V4 software.
I am using it with MVC3.
Example mvcSiteMap Code:
<mvcSiteMapNode roles="Admin" title="Your Subscription (All Users)"
controller="SOU" action="ListSubscribers">
This roles attribute value has no effect:
<mvcSiteMapNode roles="NoAdmin" title="Your Subscription (All
Users)" controller="SOU" action="ListSubscribers">
This is the same. I would expect the above to not work if the Admin was
logged in? I would expect the first example to work if only the user was
logged in.
... But no effect .
Many thanks