What is Defense of Property? defense attorney law of property is an affirmative defense used by a person in a lawsuit to state that they used reasonable force to protect their property from harm. If the defendant can prove that they injured the plaintiff only because they reasonably believed that their property would be harmed if they did not, then the defendant may not be held liable for damages even though they admit that they injured the plaintiff. Defense of property is different from other defenses such as self-defense or defense of others because the use of force must be much more limited.