You don't need expensive border security, just as the US does not need that wall.
Did you see the scenes from Ceuta? An enormous wall, with spikes on it, heavily guarded and still they are coming through.
People that desperate don't count on benefits first, most of them know exactly well that they don't have a chance legally, that's why they are hanging around the wall waiting for their moment, as the South Americans do at the mexican-US border. They don't want our benefits in the first place, they are living a dream...they want only a foot in and vanish in the land of "milk and honey", believing to find a way to earn some bucks...illegally of course...even these few bucks can secure the survival of whole families back home.
It's a dream which will end in a nightmare for most of them, we know that, most who did the trek already know that. But what keeps this dream alive are the few reports of people who "made it" somehow, even if it's exaggerated or plain lies...it's a dream!
Dreams aren't rational!
So you can't expect these people to act rational...so you will need a strict and powerful border security if you really want these people from streaming in. Arguments or benefits are not the source, desperation is, a dream is.