You forgot the mine fields.
Frankly, I have traveled big sections of the border region. Parts of that frontier are almost inaccessible by foot, let alone by vehicle. It would be cost prohibitive and unnecessary to put a fence across every single mile of the border.
That won't work. Nothing works. Just give up. It has no chance. It's too expensive. Walls don't work. You want the Berlin Wall? Next you'll want mines. You want to kill people? It won't stop tunnels. They come in by planes. Trucks. They'll use trucks. It violates international law. Give me a minute I'll have some more excuses.