Game-theoretic modelling is used to study the design of an agreement among residents to conserve a wildlife resource, by not hunting animals illegally when the community monitors its own behaviour. The analysis demonstrates that such an agreement may be very much costlier for a government to sustain if its incentive structure avoids the payment of monitoring fees, and instead relies on community benefits for conservation, with bonuses for reporting poachers. Conditions are identified for the agreement to be stable against both the temptation to avoid monitoring and the temptation to poach, either with guns or by snaring. In particular, the size of the community must exceed a critical value. Implications are discussed for community-based wildlife management programmes in Africa.