[Zope] overriding security acquisition

Hi, I'm building an app that has a security model that is a bit contrary to Zope's acquisition path for local roles. There are folders that represent 'team's, and a role I've defined of 'member'. Some teams have sub-teams, and these team folders have the sub-teams' folders within. The problem is, if I make someone a 'member' of a team by giving the user a local role in that team's folder, then that person becomes a member of all the sub-teams, since the permissions acquire upward. This isn't what I want. Is there a way to get Zope to not climb the acquisition tree when doing its local role calculations? -r