Barrier is not a wall.
Wall stops drugs and babies, slat barrier does not.
What we've seen so far of the slat barrier will be a perpetual maintenance nightmare and consequently would be a somewhat temporary solution compared to a concrete wall.
Is it possible that DJT knows that it only needs be temporary? Don't know.
Concrete would be over kill if the second coming or other 'shift' is due to happen within a few short years.