WinVolumeLock

WinVolumeLock is a lightweight utility designed to help you lock the volume on your PC. The tool can come in handy in a variety of situations, including those that imply toggling the volume by mistake, installed apps modifying the sound or other users who mess up with your settings.

The only active settings are mute and unmute

The setup is a quick and forward operation that does not require any special attention on your part. The program does not have an interface per se, but rather it creates a small icon in the System Tray. As you probably hinted, you can set the volume and then access the app to lock it. While this prevents other users and programs from altering the volume, you should bear in mind that the mute and unmute are still available.
If you prefer not to lock the volume completely, then you can use the Volume Max option. As the name implies, the feature allows you to configure a maximum volume that cannot be exceeded by other users. The option may come in handy for shared computers and particularly, if you are allowing children to access the PC, as they cannot increase the volume at inappropriate times, for instance. The utility also allows you to force the volume to a specific value, which may come in handy when listening to music or watching TV shows or movies that do not feature sound equalizer on the PC.

Unlocking can be done via Administrator accounts

Unlocking the volume so that you can make it louder or more softer can be done following the same procedure: right-click on the app's icon and access the Unlock Volume. To avoid having other users or apps change your volume settings, it is highly recommended you use the app via an Administrator Account. Therefore, only Admin accounts can unlock the volume via WinVolumeLock.