In the context of hostile reconnaissance, CPNI defines deterrence as: The intelligent, co-ordinated promotion of protective security provision to the hostile that results in the perception and/or assessment that the reconnaissance or the attack itself will fail.
Hostiles will not necessarily be automatically deterred from a target simply because it has CCTV or guards or a particular fence or lock. Instead, an organisation needs to use these security measures in an effective manner and to then communicate them to the hostile. If a hostile believes a site has excellent security measures due to what they’ve read online or seen on a poster or witnessed in operation, it may be enough to deter them from their target altogether.
Deterrent measures can be cheap, relatively easy to deploy or may just involve the more targeted deployment of existing assets. They will involve the security practitioner working with colleagues from across their organisation, most notably in communications and their ultimate effect should be one that will deter the hostile yet have a neutral or even positive effect on your employees and visitors.