You are right.. it is on an INTERFACE level, and it doesn't mean my proxy will be 'down' via interface.
More often than not, networking/connectivity is fine, but http daemon/parser is down or has an issue, say with a signature update, and gets stuck.. so you are right.. may not be the best method to add failover detection.
I'll have a look the doco you sent Steve. Thankyou very much.