Protected areas are intended to conserve biodiversity by restricting human activities within their boundaries. However, such restrictions are difficult to enforce fully in many tropical parks. Improving regulatory enforcement requires an understanding of prevailing challenges to detection and sanctioning activities. Drawing from empirical field research in 15 Colombian parks, I show that current enforcement efforts may be insufficient to deter most priority threats. For long-term infractions, such as agriculture, livestock grazing, and construction, sanctioning violators is challenging, whereas for furtive infractions, such as logging and hunting, it may be difficult to detect violators. Investment in staff, equipment and infrastructure may fail to increase enforcement capacity and yield positive conservation outcomes unless accompanied by resolution of land tenure, clarification of use rights, improved patrolling strategies and protection of park guards.