The COVID-19 pandemic has brought biosecurity to the forefront of national security policy. Land use change is a fundamental driver of zoonotic disease outbreaks, yet substantial study is yet required to unravel the mechanisms by which land use-induced spillover operates. Ecological degradation may be the 21st Century’s most overlooked security threat. Within the biosecurity context, we introduce ecological countermeasures as highly targeted, landscape-based interventions aimed at arresting one or more of the components of land use-induced spillover, the chain of biological events that facilitate large-scale outbreaks of diseases transmitted between wildlife and people. We provide case studies of ecological countermeasures of particular interest to the US Department of Defense, broadly discuss countermeasures in the defense and health sectors, and provide an overview of recent US policy decisions related to health security in order to underscore the need for greater attention to ecological resilience as our best defense against future pandemics.