These types of things are effective at the margins. Make it a little harder, and the people who don't want that hardship will avoid it, but the people willing to endure it will. Make it even more harder, and even fewer people will endure the hardship. A longer wall will be effective at the margins. Putting a longer wall at all the crossing points makes people go further into the wilderness, and makes it easier for border guards to guard the border.
Anyway, I just didn't see how the wall would be ineffective. Sounded like your standard for being effective was a little high, as in, you expected perfection, and since we can't achieve perfection, why try.