Physically Non-excludable Resources:

Physical non-excludability arises where it is not possible or reasonable practicable to exclude strangers from access to the benefits of a particular resource in its existing form...

A second species of non-excludability takes the form of legal non-excludability. It is frequently the case that a resource is protectable against strangers by legal means, such measures often taking the form of binding contractual stipulation or the adoption of a particular regime of intellectual property. If, however, the plaintiff fails to use such means, where available, to regulate the access of strangers to the benefits of a resource, then the resource must be deemed non-excludable in relation to those strangers who actually succeed in gaining access. Just as in the instance of physically non-excludable resources, the risk of legal non-excludability rests with the plaintiff who seeks to propertise a particular resource. The plaintiff who neglects to utilise relevant legal protection has failed, so to speak to raise around the disputed resource the legal fences which were plainly available to him. He has failed to stake out his claim; he has failed in effect to propertise the resource.