SyncThemCalendars allows you to set up a sync between two calendars in order to copy events from one calendar to another.
It basically allows you to block time in one calendar based on events from another calendar. That way, you can have the target calendar reflect your true availability, and never get double booked over meetings you have scheduled on different calendars.

This is a must-have tool for consultants who need to manage several calendars with their different clients.