how prevent IP conflict

[Pol Hallen]

Hi all, I'm sorry for question but I didn't found a correct way to solve
my problem.

I've a small lan (less than 10 machines) 192.168.1.0/24 and one server
(192.168.1.200)

dhcp runs perfectly but someone (for stupid game) put his machine to
static IP address: static same IP of server, lan goes down.

So, what's the best choice to prevent this situation? Do a subnet?

Thanks for help!

Pol