Trump also proposed digging a water-filled moat and stocking it with snakes and alligators. If he was kidding, his aides didn’t think so, as they sought a cost estimate for the cartoonishly ludicrous proposal. Trump also wanted the wall to be electrified, and topped with spikes that could “pierce human flesh.”
He’s made this “joke” before.
Source
8 year old boys come up with more fleshed out defenses
To be fair, Trump did say that he’s the same as when he was 6.