Conservation planning studies typically treat threats as exogenous and evaluate siting rules from a planner’s perspective. We argue that conservation is often contested, and develop a sequential land-claim game that models conservation as a dynamic, adversarial contest between conservationists (“Greens”) and developers (“Farmers”). We explore the framework in a Claims World that isolates the role of rivalry and leakage, and in a Budget World that introduces procurement constraints, decomposing outcomes into a Pure Strategy Effect (PSE)—the intrinsic quality of sites a strategy targets—and a Displacement–Leakage Effect (DLE)—the spillover gains from displacing developers’ preferred sites when leakage is incomplete. Our results generate several counterintuitive patterns. First, the link between threat-weighting and additionality breaks down once developer adaptation is allowed. Second, reducing leakage can paradoxically increase misallocation. Third, the textbook ratio-greedy rule (maximise efficiency) is systematically dominated by the simple value-greedy rule (maximise environment): we explore this ‘knapsack reversal’ more formally and show how it can produce a ‘disappointment gap’ between static (Marxan) planning and dynamic implementation. We then transport our dynamic contest to a Bolivia-based planning board constructed from biophysical data and confirm that the qualitative rankings from the simulations carry over, and adversarial outcomes lie well below the static cost-effectiveness upper bound. Tiny-grid equilibria, formal analysis and robustness exercises in the Appendix show that these patterns are consistent with best-response logic rather than artefacts of modelling choices. Together, the results suggest that robust conservation in contested landscapes requires strategies that anticipate adaptation, not just static threats.