Let's look at the nature of force first. First of all let's get our definitions straight, we're talking about physical force brought to bear upon one person by another, or group of others.Within this framework there are 3 distinct types of force.
Type#1, initiatory force. Example: you're walking down the street, and someone out of the blue hits you, let's say in an attempt to steal your wallet. You have done absolutely nothing wrong, and in no way deserve this to happen. In fact there is no instance whatsoever in which initiatory force is justifiable. If the perpetrator is caught and convicted he goes to jail and rightly so.
Type #2, defensive force. Example : the guy who hit you to take your wallet is a pansy, and his blow has little effect upon you. You turn and break his jaw with a left hook, dropping him like a bad habit. Bravo! Well done, because defensive force in this, and any other instance in which it is warranted (by having force initiated upon you) is not just acceptable, it is a moral imperative, assuming you value your own life and well being above that of your attacker. On a personal note, if you don't value your life and well being above his, seek professional help!
Type #3, retaliatory force. Example : the guy knocks you out and gets your wallet, but you recognized him and know where he lives. As soon as your head clears, you head over, kick in his door, and catching him off guard you knock him out and retrieve your wallet. This type of force is a bit tricky, because while it is a natural right to do this, as members of a society built upon laws and due process we have delegated the right to this type of force to governmental agencies, ie, police, prisons, armed forces, etc. We haven't given up the right, but in the interests of societal harmony we have these systems in place . So since within the confines of a civilized society retaliatory force is the exclusive province of the government, if you get caught you go to jail and rightly so.
Applying this to the situation of a landowner, what is the justification for bringing force to bear against someone who has done nothing wrong except buy a piece of property that someone for some reason considers choice in some way?