If they are changing it with AirPlay that means they are on the same WIFI network. Is this strictly necessary? Do you know the people well? Maybe just ask them to not mess with your speaker? As far as I know there is no way to disable AirPlay itself on the speaker. 

Hi @DBurke67 

Welcome to the Sonos Community!

As ​​​@Whistler alludes to, you can tell your router to set up a guest WiFi network - devices/people connecting to it have no access to other devices on the network, only to the internet. How exactly to do this varies with each router, but if stuck, you can ask your Internet Service Provider or router manufacturer for assistance.

If guests already know your main WiFi credentials, however, you will need to change them for this to work effectively, which means you will also need to update all your devices with the new details, including Sonos. See our Connect Sonos to a new router or Wi-Fi network help page for how to do this with Sonos.

I hope this helps.

Many routers also let you blacklist certain devices from access.  I know Comcast allows this.