How to protect data when OpenVPN breaks?

Question

linux

Good afternoon.
There is Ubuntu. If the OpenVPN connection breaks, then all traffic goes directly.
How to make it so that nothing works when it breaks, including DNS?
That is, only OpenVPN connection and 8.8.8.8 dns are allowed.
Please write more detailed answers. I have been trying to solve the issue for a long time.

Answer 1

Remove the default route from the interface with the Internet after raising the tunnel.
Script:

#!/bin/sh
ip route del default dev dev_name

Answer 2

What's stopping you from configuring the "gufw" firewall?