How to secure users

hi there

i have 1 mikrotik router OS on PC with level6 , i have a LAN with 600 customers, and they are all in one Vlan on switch’s , we give them ip with dhcp ( dhcp service is on mikrotik ) , and they connect with pppoe connection and reach the internet, and question is , if sb in our lan set static ip on the pc like 192.168.0.1 and then another person do something like this they got an ip conflict in this situation i want to in separated Vlans to prevent of this problems and they cant reach another pc’s in LAN

what should i do?

thanks

you can read fromthis web http://mikrotik.unimedcenter.org/mikrotik-firewall