I think you completely misunderstand why people build fences or walls around their homes.

House wall: - keep pesky neighborhood kids from running through it and ruining your grass - keep your neighbors from being able to see you while youre swimming in your pool

Border wall: - attempt to keep Mexicans from immigrating into the country illegally

I fail to see how these use cases are at all similar. Please, if I missed a use case for a house or if your home is constantly being attacked by barbarians let me know, but I don't think anybody in California builds a wall to "defend" themselves.