How to cause a failover to another server when a error string is present in a response?

Yeah, as it turns out, the health monitors looking for a string that is always there when the sites are up is a better choice. Thanks for all the suggestions though; the performance hit of looking at every response was the first thing that came into mind that made it seem unpalatable, but i proceeded with the assumption that there were either efficiencies in it I was not aware of yet, or there was just a better way to do it.