How about using our on-premise poller. This would give a full fledged monitoring for your local url, I am sure you are aware of it. I would recommend using this instead. It includes a variety of configurations, including content checks like Should contain string(s), Should not contain string(s), Case sensitive, Should match regular expression and a lot more...
I would recommend to form a monitor group of servers and the on-prem url and use the dependent monitor feature. That way when the url is down it will check for the server and then check for the url.
Hope it makes sense. If this is not the case, let us know the scenario so that we can check how best we can solve it.