Implement DLP (Data Loss Prevention): DLP solutions monitor and control data transfers within a network. They can help organizations detect suspicious activities that could indicate data exfiltration, unauthorized data access, or other potential insider threats. DLP can be configured to flag or block sensitive data transfers or unauthorized activities, making it a targeted solution for detecting insider threats. 

Regularly rotate passwords: While this is a good security practice, it's not specifically designed to detect insider threats. Password rotation makes it more difficult for attackers to use compromised credentials, but it doesn't prevent or detect malicious activities from authorized users (insiders) who would know the new passwords. 

Mandatory vacations: This is an old-school tactic designed to catch fraudulent activities by forcing employees to be away from work, making it more likely that irregularities will be noticed in their absence. However, this is not a systematic or particularly effective way to detect insider threats on an ongoing basis. 

Increase perimeter defenses: Focusing on perimeter defenses like firewalls and intrusion detection systems (IDS) is typically more effective against external threats. These measures are less useful for detecting insider threats, who often already have legitimate access to internal resources.