How to block OTHER DHCP servers?

I am setting up a new WiFi network and I am using the ER-5poe.

I have:

eth0 as the WAN with a public IP

eth1 unused but will eventually use it as a way in from the customer's subnet.

eth2,3,4 configured as switch0 for the WiFi network.

I am trying to block any DHCP servers on switch0 that are not the ER-5poe. Is this possible?

If yes, can you provice some basic idea for how to setup the rule?

Thanks,

Jason