Mixing : Automation : Automation Preferences : Automation Safe

Automation Safe
Outputs, sends, and plug-ins can be placed in Automation Safe mode. In Automation Safe mode, any automation associated with an Output window (such as track or send level, panning, or mute), or plug-in on that track, is protected from being overwritten while automating other items on that track.
 
Automation Safe mode suspends automation recording for the selected track output, send, or plug-in that is enabled. You can also suspend automation recording and playback session-wide from the Automation window. See Enabling and Suspending Automation.