You can use VPC Service Controls to secure your Cloud DNS configuration.
VPC Service Controls provides additional security for your Cloud DNS to help mitigate the risk of data exfiltration. Using VPC Service Controls, you can add projects to service perimeters that protect resources and services from requests that originate outside the perimeter.
To learn how to configure DNS using Cloud DNS, see Configuring DNS with Cloud DNS.
To learn more about service perimeters, refer to the Service perimeter configuration page of the VPC Service Controls documentation.