root-guard

[mohamed_el_harr]

Hi all,
Ruckus says about root-guard that: "Root guard must be configured on the perimeter of the
network rather than the core."
But as far as  I know the root guard should be configured on the core switch (most of the time the core switch is root Switch for the STP)  to prevent any superior BPDU to come from the Access Switches.
any explication about this quote??
Thank you