I stand by that and don't believe we're talking about the same thing here. Technology has changed greatly but, getting all the illegal to come forward [or simply find them all] is still the greatest barrier.
Thanks to the inaction of the last two Admins, we have no idea who is actually in this country.
We need to secure the border first.
Well, start by enforcing the laws we have. We can't secure much of anything if the Government won't prosecute, won't allow local LEOs to hold illegals for deportation (that gets into Federal turf and is a no-no). It won't happen with sanctuary cities, either.
If there is no enforcement, even if the 1954 miles of physical and 'virtual' barrier were built, we'd still be stuck with all the ones who are growing more entrenched by the day. There are places a physical barrier can be erected. The places it can't (which will more likely be ingress areas) can be monitored by virtual means, but without boots on the ground, and the ability to enforce the law, that will be meaningless.