The type of network that can be secured entirely through physical safeguards is a LAN (Local Area Network).
In a LAN, you have direct control over the physical environment, including who has access to the network devices and cabling. Physical safeguards such as locks, surveillance, and controlled access can effectively secure a LAN.
On the other hand, WLAN (Wireless Local Area Network), WAN (Wide Area Network), and VPN (Virtual Private Network) have components that are more challenging to secure solely through physical means, as they often involve wireless communications and connections that extend beyond a single physical location.