If you’re looking for anonimity of data, think of implementing an IpSec VPN.
If you’re looking for network availability, think of redundant links, link controllers, Service Providers redundancy etc
If you’re looking for authentication into the network, think of NAC, or some kind of IAM
If you’re looking for data leak prevention, start implementing some technologies that analyze SMTP and WEB trafic to detect data exfiltration and user behaviour analytics.
Also, it’s good to think of network segmentation using DMZs and VLANs in order to separate network flows that doesn’t need to interact
So it really depends on your needs and your budget.