Prevent IIS from unloading ASP.Net site

How do I prevent an ASP.Net site from being unloaded by IIS?

I have what may be the dumbest website in the world - once per hour it wakes up and writes a timestamp to a log file. When the app starts, it says so with a timestamp in the log, and when it dies, same thing.

In IIS I went into its Application Pool and set the Idle Timeout to 0 and set Generate Recycle Event Log Entry > Regular Time Interval to False.

Yet the site still unloads itself about once per day - I get the App Unloading... entry in the log and it sits dead until I next visit it.

How do I prevent it from unloading?

(Obviously this site will do more once I get this resolved - for now it's as simple as possible to isolate the problem.)