Possible to configure router to use pi-hole as primary DNS but also define a fallback in case pi-hole box is down

[Mcat12]

See here why you can't designate a certain server as primary:

Primary vs. Secondary DNS

Hi, small question: I have set OpenDNS as primary DNS and Google (8.8.4.4.) as the secondary one in PiHole. I always thought that the secondary DNS is a fall-back solution; only used in case the primary DNS fails. However, looking at the admin page it seems that the Pi is simply using both at the same time. The primary DNS gets about 60% of the queries and the other 40% go to the secondary one. Why is this? Now I'm wondering if my Router, which has a secondary DNS set in case my Pi goes down,…