Only by blocking users from that network. Unlike “regular” AirPlay, Sonos AirPlay requires access to the same network as the Sonos devices.

Thanks for the fast replay!

That is a pity… Is it possible to add this request to a future enhancement list? 
 

The Sonos trust model is based on your network: if you trust people on your network, you trust them with access to your music devices.

People have asked for more granular security many times in the past, hasn’t happened yet.