Rather than sharing your calendar with everyone at your organisation, you can choose specific people to share with. You could also share your calendar with everyone, then allow access to additional people outside of your organisation.
To share your calendar:
Under My Calendars, position the mouse over the calendar you wish to share, then click on the ellipses that appear
Choose Settings and sharing
Under Share with Specific People, click on the Add People link
Type the name or email address of the person you wish to share your calendar with
Select the required person from the list of suggestions
Choose how you wish this person to be able to access your calendar (see table below), then click on Send
When adding specific people to your calendar, you can choose the following permission settings:
If you no longer want a colleague to able to access your calendar:
Under My Calendars, position the mouse over the calendar you wish to share, then click on the ellipses that appear
Choose Settings and sharing
Under Share with Specific People, click on the X to the right of the name of the person you wish to remove from your calendar