Restrict Access to Business Rule for Administrators

Anyone in the native "Administrators" security group is going to have access to BRs, no matter what you do. That is just because there has to be at least one person (e.g. native "Administrators") that have access to see everything.  Otherwise you would tie yourself up.

You can create a paired back Admin group to whom you grant access to certain application elements and in doing so restrict those Admins from getting to the business rules page but keeping this security group as "Administrators" and not placing them in the native admin group:

You could also allow them to get to the business rules page and then within each business rule change the Access and/or maintenance group to now allow them to see BRs.  But this is tricky because that means anytime you load up new tools and BRs, you have to circle back and change each BR's individual security properties: