​The first piece of a physical protection system that comes into play, whether in deterring an intruder or attempting to stop the attempt at intrusion, is the perimeter barrier. This barrier can take many forms, from a fence or wall meant to physically obstruct entry, to signs that deter trespassing by ensuring property boundaries are known.
 
As with all elements of security, the best solution will vary based on the environment and the purpose of the property. In some cases the threat level is low enough that simply marking the area the owner does not wish to be crossed is enough to stop intrusion, or more there could be a worry that more oppressive measures could ward off potential customers.
 
In other cases, the threat level is high enough that more defenses are needed. To an extremely motivated intruder, a fence or wall will only delay their entry. However, as one of many delay barriers to be overcome, in addition to the ability to limit access points to certain areas, perimeter barriers remain a significant element in both deterring and stopping intrusion.
 

​In an ideal situation, the security of any location will be first considered while the design of the property is being first created. Many environmental factors have a large influence on the potential protection plans that can be implemented there, even things that may seem unrelated, such as vegetation.
 
A fence or similar barrier may help in securing a location by deterring intrusion or limiting traffic to particular areas. It may also hinder security by limiting visibility. In addition, if a fence or other security measure may not present the image that an owner wants for his property, and a security operation should not hinder normal operation.
 
Unfortunately, factoring in a protection plan while designing a property is a relatively new concept, and many businesses are based in older facilities that have limitations that need to be worked around. However, every property likely has some room for improvement that can be revealed by comprehensive evaluation by security professionals, even if it as simple as increasing lighting levels in the right area.
 

​The criminality of an individual is by itself not sufficient for a crime to occur. Though in many cases, a criminal will be so determined to commit a crime that it will be impossible to deter, the circumstances of the situation and environment need to have certain characteristics for a crime to be possible.
 
Situational Crime Prevention works on four principles: that if the effort needed by the criminal to commit the crime is increased, that if the risks to the criminal during perpetration are increased, if the potential rewards for the crime are reduced, and if the excuses to plead ignorance of the act being illegal are removed, then the likelihood of the crime being committed drops significantly.
 
In many environments it is impossible to remove the assets on site that make tempting targets for an intrusion. That leaves the best path to stopping one to be making it clear to the potential intruder that his goals in theft or vandalism will be extremely difficult to achieve, and impossible to do so without being identified. With hardening measures such as physical barriers and access control systems, and highly visible surveillance by cameras, or most effectively by live personnel that can react to an situation immediately, almost any area will be passed on for a more vulnerable and less intimidating target.