You hit the nail on the head. This is the relevant question. Of course we have states and they do both enforce and sometimes create rules. That is why people l

You hit the nail on the head. This is the relevant question. Of course we have states and they do both enforce and sometimes create rules. That is why people like Hayek and many others were not anarchists. The hole philosophy of classical liberalism is based around the idea of a small state to enforce these rights. The problem is that the solution 'the state' is not a complete one. We of course also know that property rights do exist and persist outside of state systems. Many different types of system can and do provide rights and have mechanism for enforcement. It is a major field of study in both economics, for legal scholars and many others. There has been a lot of work on this question and it is a hard one to answer. One possible that one economist/legal scholar provides is that it is all about the Schelling point, you pick some point and commit to overreaction. Once you have this idea even two people on a empty island can establish property rights. So its about commitment and signaling. We can easily find situations like this in real live. There are tons of example both now and historically. Common Law for example was not created by the state, but was in essence eventually enforced by the state. The first Stock market in Amsterdam was neither created, nor enforced by the state. There is a hole lot to be talked about. To tie it back together with the original discussion. If we are talking about pollution protection in the current world, it would of course have to be either rules created by the state, or rules that evolve as they did in common law (in fact many rules already exist in British common law). The state could set the limits for a pollutant but then let it be enforced by normal law enforcement, more like civil rather then criminal law. P.S: Many classical liberals believe in Natural Law, but many also do not. This debate is still active and has not gone away.