This paper uses replicator dynamics to compare the steady states arising from two types of common property regimes - one in which over-exploiters are punished by the resource users themselves, and another where enforcement is handled by guards who collect a tax from the users. The use of guards requires a less restrictive set of parametric conditions in order to maintain an equilibrium with no over-exploiters. However, it can also stabilize an outcome in which all users over-exploit and are punished, but not enough to induce more cooperation (less resource extraction). These results can be used in guiding and structuring the formation of new common property regimes.