I don't think it was at all secret.
In a campaign, politicians give simplistic messages. Saying "wall" is exactly that.
But every sentient voter sees thru that, expecting implementation to be more complex.
The "wall" being obviously a slogan, it's obvious even to the most casual observer that
there are locations where the terrain itself presents a good physical barrier, & that in such
places, a patrolled border with sensors would be most cost effective. If this is obvious to
even me, then it would be so to Trump & his associates.
What evidence do you have that I'm wrong?
After all, my "wall" expectations have been borne out, unlike yours.
Too many anti-Trumpers get caught up in their own histrionics....."he's stupid"...."he's
irrational"....he's <insert insult here>. They get caught up in believing such rhetoric,
but then they underestimate him. Don't be one of them.