Net Cut Problem

I have net cut problem in network, I thought that if all users will have ip address 192.168.0.0/30 this problem with net cut will never appear, so i want to block only that ip that are not using ip with mask 30 (255.255.255.252), but when i do this with firewall other clients with mask 30 have problems, i think i need some specific configuration anyone can help me? with firewall configuration

http://forum.mikrotik.com/search.php?keywords=netcut

http://forum.mikrotik.com/t/32-subnet-mask-to-prevent-arp-spoofing/26921/1