Indeed, it's like people completely forget about such attempts in the form of the Berlin-wall or the border between the two Koreas.

Heavily militarized borders with everything technically possible defending them, regardless of inhumane it was/is, yet didn't stop people from attempting to cross and actually crossing.

Even the great wall of China isn't a good example because afaik that wasn't built to stop immigration, it was built to stop raiding parties.

It doesn't need to be perfect. Nobody is arguing for it to be impenetrable, just better secured than it is.