Dual Wan ddns setup

[vonedaddy]

So I have pfsense running with a dual wan setup.  I call them FASTWAN and SLOWWAN.  I have pfsense configured for load balancing and failover (see screenshot of gateway groups).

I have DDNS setup through no-ip, but I only want the dns name to point to the FASTWAN.  I selected FASTWAN as the interface to monitor in the dynamic DNS setup, however it is still occasionally updating DDNS with the SLOWAN IP address which is breaking my VPN.

Any ideas?

I was thinking I could solve it with a firewall rule, but that seems hackish.