Roles and permissions

I need to create two different Admin roles on a site:

1. PRI_ADMIN: 100% access and permissions to the site

2. SEC_ADMIN: Default administrator BUT must can't modify or assign to PRI_ADMIN role.

I tried to edit the SEC_ADMIN role:
- Create and manage roles = Prohibit.

This doesn't seem to make ANY change at all...? I can still use this role to edit all other roles (including PRI_ADMIN)...

So, is it possible to these to admins?

Best regards,
Ole