Most likely: you'll stop only 10%, and divert 70% to over-the-beach entry, which the USCG cannot cope with as it is. So,
Union labor? Who need union labor?
Ever hear of the Davis-Bacon Act? Of course you haven't.
we have the SeaBees and the US Army Corps of Engineers.
The Army Corps of Engineers is all civil service and union contract labor.
And the there aren't enough Seabees available for this mission: they're already committed to other taskings that support the US Navy.
We have prison labor.
Prison labor to build something deemed vital for national security...
With all due respect, that is a really foolish idea.
We have hundreds of thousands of illegals sitting on their butts in jail.
And I'm sure they'd do good quality work on the wall intended to keep them out...
Another really foolish idea.
We have contactors who are employing illegals and can be court-ordered to work for nothing as part of their restitution for employing illegals, in lieu of jail or closing them down, using those same illegals prior to deportation.
Except that those contractors never get convicted in the first place--juries consistently refuse to convict people for hiring day laborers.
29 CFR 1.7 (b) If there has not been sufficient similar construction within the area in the past year to make a wage determination, wages paid on similar construction in surrounding counties may be considered, Provided That projects in metropolitan counties may not be used as a source of data for a wage determination in a rural county, and projects in rural counties may not be used as a source of data for a wage determination for a metropolitan county."
(the term "may" is permissive (i.e. Not legally binding) and I don't think that there have been "prevailing wage" national border wall projects across the sonoran desert in the last year, nor does David-Bacon apply to prison labor or the US military. IT isn't that difficult to trench down 6' and stand 20' pre-cast, reinforced concrete slabs on end, then backfill. Cast steel plates into the concrete and weld them together with 6" between for water and animal passage. Where we can't trench, razor-wire entanglement-topped and bottomed welded 100 lb. landing mats secured to posts and buddy we can put posts ANYWHERE. Look at freeway fences. Let's say we can only wall 60% of the border. That leaves 40% upon we can concentrate our primary forces, with rapid response units triggered by electronic observation posts on the walled/solid-fenced portions. Nothing is 100% effective but even 30% (and I believe your number to be Wa-a-a-y low) is better than 100% INeffective, which is where we are right now. Add to this, placing a Federal bounty on invaders rather than punishing those who detain them, and this problem would dry up in WEEKS, with or without a wall.