An empty gesture?
Let's do away with all law enforcement then, it's just an empty gesture after all. It's not like they deter anyone from breaking the law.
Seriously though, I doubt a group of would be invaders would cross the fence if they knew a squad of border troops were watching them. If they tried, we could use some of our knew nonlethal sound weapons on them. The kind that makes people unable to stand up and defecate on themselves. Once incapacitated, they could be rounded up and put back on their side of the fence.