DDNS resolvers are inadequate for certain deployments involving double NAT (such as satellite connections) or very fast-changing WAN IPs (as with trains or other high-speed travel).

Fail-Open Relay

DNSFilter needs develop a fail open relay service for when DDNS resolvers don't work.

This solution would work similar to ScoutDNS's relay solution pasted below.

"When enabled, the ScoutDNS relay will no longer depend on any known WAN IP interface after its initial cloud-based adoption. Instead, the relay will use a unique identifier, similar to our roaming clients, to track usage. This usage remains linked to the site or location for logging purposes, so no site or query visibility is lost. Relay deployments on mission-critical networks can now enable the fail-open state on their relays. This allows you to configure up to four third-party DNS resolvers as fail-open upstream services, providing maximum uptime protection against localized and regional peering issues."