failover on a multi-homed PC

When a PC is attached to two networks and both networks use DHCP,
Windows will discover a default gateway on both networks (as shown
using the ipconfig /all command)

Whichever network is selected by Windows to be the system default will
determine which default gateway Windows uses. (I can use the Metric
to influence this selection)

My question is, if the network cable attached to the interface that
provides the current default gateway is unplugged, Windows will switch
over to using the default gateway on the other interface. Is there
any way to prevent this from happening?

I have a LAN (LAN1) which provides general purpose connectivity and a
LAN (LAN2) which provides only a single device. When the cable is
pulled from LAN1 I do not want Windows to begin routing traffic to the
LAN2 default gateway. Is there a way to stop this?

Sending LAN1 traffic to LAN2 is causing problems because the single
device there does the DHCP, the DNS, and is a provider of data. The
poor little device gets overwhelmed when it is flooded with
unnecessary DHCP and DSN requests.