There are lots of tools around to help people carry out ARP-related exploits and if a malicious, Wi-Fi enabled neighbour decided to find out more about your network, this could be an effective way to do it.
The good news is that there are some defences out there. The bad? They can be costly and don’t always deliver the protection you might expect.
Arpdefender is a good example. It’s a solid-state security appliance that you simply connect to your network, then leave to look out for ARP poisoning attacks. It would be excellent if not for the fact that it costs almost £300 and, even if it does detect an attack, will do little more than make an entry in your system logs more