Dynamic DNS update triggers?

[gtr33m]

As I have moved from a self hosted DNS to a remote DNS I would like to replicate the failover that I had in place with the pfsense DNS package.

I have a dual WAN setup with a static IP on each WAN which I would like to have update the remote DNS server when one of the connections goes down, or ideally I would like to have it update based on a slow ping time.

I thought of using the RFC 2136 section of the Dynamic DNS module, but I don't know what triggers and update.  The online manual states on PPPoE login or IP change, but would that include a connection loss, and more importantly what IP would it send?

If I setup 2 services, one for each WAN connection, would the Dynamic DNS remove one of the entries if the link went down?

Even better, would there be a way to customise the module to send one IP depending on the ping time, sending the one with the lowest ping so that my fastest connection is always the one served?

Thanks,

Mark