Function to toggle between two values of an enum
Would there ever be a need to add more values to the MonitoringMode enum?

enum MonitoringMode
{
    Seek,
    Destroy,
    Something,
    SomethingElse
}


In that case, you're not "toggling" - you're mapping. And there's a data structure for that:

private static readonly IDictionary ModeMap = new Dictionary&lt;MonitoringMode,MonitoringMode&gt;
{
    { MonitoringMode.Seek, MonitoringMode.Destroy },
    { MonitoringMode.Destroy, MonitoringMode.Seek },
    // ...
};


Then you could switch from one value to the next simply by using that map:

void ToggleMonitoringMode()
{
    _monitoringMode = ModeMap[_monitoringMode];
}




If there's not going to be a need to ever add more values, then I'd question the use of an enum type here, because you're really toggling between true and false states of some _isSeeking Boolean, which you already know how to toggle.