Me and a lot of other voters. People aren't dumb - they know what methods are effective and which ones aren't. Patrols are only as good as the desire of those in charge - a wall works 24 hours a day.
You do know that a wall to keep people out can also be used to keep people in don't you?
Actually, a fence does not work 24 hours a day because an unpatrolled fence will be dug under, climbed over, broken through, etc. It might help but I suspect being caught and arrested or sent back by a human, is the surest deterrent.