I use DNSimple and they have a feature that lets you sync to another provider. I have not used it but, as I understand it, the feature helps you setup slave se

I use DNSimple and they have a feature that lets you sync to another provider. I have not used it but, as I understand it, the feature helps you setup slave servers which respond to Notify messages from DNSimple. That way, if they go down, your slave provider will keep things up.