True DNS Backup

[Mike]

Hello all, I have a question about how best to set up dns for fast recovery 
in case one fails. Here is my scenario: I'm also using fictitious IP 
addresses to make it easier to explain.

I have two internet routers 1 each from different providers. The first has 
network of  1.2.3.0 the second has network 8.9.10.0
The two servers run bind v9. The primary dns has an IP address of 1.2.3.1 
with a secondary IP of 8.9.10.1
The second dns which is slave to the primary has an IP of 8.9.10.2 with a 
secondary IP of 1.2.3.2.

Ok here is my real question. If network provider network 1.2.3.0 fails I 
want the dns servers to continue serving dns. If network provider 8.9.10.0 
fails I want the dns's to continue serving dns. If I have the servers set up 
this way will it work? Or does anyone out there have a better way of doing 
this. Any help appreciated.

Thanks