Bacteria often produce public goods that benefit the population as a whole. This type of behavior is vulnerable to invasion by cheating bacteria who do not produce the common good. Barring defense mechanisms, this will lead to the collapse of the entire population of cooperators and cheaters alike, a phenomenon known as the Tragedy of the Commons. In this talk we will discuss a particular ``policing" defense mechanism to avoid the Tragedy. A subgroup of the population, called ``the police", will produce a toxin that kills all non-policing cells. Provided that the killing rate of cheating cells is sufficiently high compared to the killing rate of cooperating cells, we shall see that this enables the population to resist invasion of cheaters, and avoid the subsequent Tragedy of the Commons.