you can start with finding out total devices you have for your whole household. can set dhcp allocations to that number and set all devices in router as static allocations.
also you could set your dhcp server to include arp on all connections fso say he added himself to the dhcp list by manual assign it still wouldnt let him on the internet as the router would look for all the connections having the arp designation.
theres other ways you could do it but it would also depend on your hardware used and your level of understanding on it all. plenty of guides tho. if you have the panaramic wifi router cox provides im not really sure what you can do as i currently use a mikrotik router and ubnt switch.
