How to check network for rogue hubs or switches

Is there a way to check whether someone has secretly plugged in a hub or switch somewhere on my network without  my knowlege?
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Implement port security on your access switches and have it learn mac addresses for each port.  Set the maximum number of macs and if the limit is exceeded, set the port to be shutdown.  What type of access switch are you using?
deshi777Author Commented:
Cisco 6509 core and 2948/2924 perimeter switches.  I understand your advice but I'm not very savvy with configuration (short of changing vlans and so forth).  Thanks.

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