Actually, the net migration has been 0, so I’m not sure where you are saying it’s 5%. Yes, some come in, but it is now reduced to the rate that they were deported (under Obama, and already it looks like a LOT more will be deported under Trump) meaning we will have be reducing the number. There’s no need for a wall.
And a wall is silly anyway. We already have more officials and drones going over the border. If people really want to find a way in, they will. And don’t forget that even though the coast guard patrols, there are MANY water ways in. A wall will do nothing there.