Property rights are collections of rights. In the first place: for something to be your property you must have the right to use or enjoy that thing. In the second place, you must have rights of control: rights that others not use or enjoy that thing in certain ways, except by your permission. Thirdly, though perhaps not necessarily, you must have the right to transfer the former two rights to someone else (as when you give your property to someone else) and fourthly the right to some form of compensation should someone infringe the preceding rights. Each of these rights, moreover, might be divided and limited in various ways. You may have the right that others not walk on your property, but not that others refrain from burrowing underneath it or flying over it. You may have a right to cultivate your own garden, but not to grow opium therein.
And so on. Acknowledging all this complexity, let us set it aside for now and focus on clear cases of the least complicated sort. I have an apple in my hand. I may eat if I choose, use it to make a pie or cider or let it rot. I may give it to someone else. You may not eat my apple without my permission. If you do so, you will have done something wrong and you will owe me compensation. All this because the apple is mine.
What are property rights? Where do they come from?
According to Retributive Ethics, moral rights are merely warrants for violence. All rights are Retributive rights: rights to harm other people. So when a Retributivist hears a right asserted he asks only who is claiming a moral permission to hurt whom, by how much and when.
In the case of property rights the question has clear answers: property rights at least include rights to defend your property: that is, to do harm to those who attempt to deprive you of its use and the right to forcibly interfere with others if they should attempt to use it without your permission. You may interfere with them by building fences or locking doors or by putting your body in their path. Should push come to shove, you may push and shove or, if society recognizes your property claim, you may call on the cops, who will do the pushing and shoving and, if need be, shooting on your behalf.
You are in short, entitled to enforce your property rights. "Force" being the operative word.
Now, academics are apt to grow faint at the first mention of violence so let me quickly offer some palliating remarks for tenured readers. Note first of all that acknowledging a right to defend property does not require you to think property rights warrant absolutely any degree of violence in the defense of absolutely any property. You may not think it permissible to shoot a burglar if you do not have much worth stealing or even if you do. You may yourself be so passive or pacifist that you would not lift a finger to protect your belongings. You may be so empathetic to the plight of those driven by circumstance to theft that you wouldn't even call the cops. Never mind. What matters is that you agree that having property makes it sometimes morally permissible (however personally repugnant) to forcibly interfere with others in some ways that would not be permissible if you had none. To deny this-- to say that it is always morally impermissible to lock a door, build a fence, or lift a finger (even to dial '911')… to defend one's property seems to me to simply deny that there is any moral right to property.
Note too that acknowledging the right to enforce your property claims does not presuppose that property rights, or any other rights, are in any sense "natural". Even if you think that the rules that govern property acquisition and ownership are as arbitrary a social artifact as the rules of NFL Football, you must nevertheless recognize that our adoption of those rules makes certain kinds of violence permissible. Neither the lineman who tackles the quarterback nor the cop who tackles the purse thief is doing something morally wrong. So even if you think "the possession of property under the law" is as inherently amoral a notion as "possession of the ball in football", you must have some account of how the violence of the lineman and the cop come to be morally permissible.
If we agree that property rights at least include some kinds of permissions to use force the next question is whether they include anything more.