arpcheck checks /proc/net/arp for MAC/IP combinations and compares them to a static list (shorewall style) or a dynamically learned MAC list. If a rogue MAC/IP is found, arpcheck alerts you.
You can download it from the following link: https://packetstormsecurity.com/files/download/42780/arpcheck.sh.txt
Source: https://packetstormsecurity.com/files/42780/arpcheck.sh.txt.html