Zend certified PHP/Magento developer

failover for incoming connections

I’m hosting a web site. One domain name. One static IP, one ISP. If this ISP goes down, how can I automatically switch to a secondary ISP and it’s static IP to access my web site? I can setup my router for failover ISP1+ISP2, it is good for redundant outgoing internet access, but for incoming access it is not good.