Check for mac address on network with Ethernet, Yun or Wifi

I'm thinking up a project involving some geo fencing, would it be possible for an arduino (a yun or uno with ethernet or WiFi shield) to check which devices are connected to the network and then act if a specific mac address is present?

Finding devices (mac address) that is connected to an existing wireless network (Plan A)

http://forum.arduino.cc/index.php?topic=292465.msg2043503#msg2043503

Finding devices (mac address) Plan B -Plan D

http://forum.arduino.cc/index.php?topic=292465.msg2313939#msg2313939