It is now common practice, that some time after a segment is completed, accepted by the Government Quality control folks, and the Contractors have cleared the area, that Military units are scheduled to come in and add concertina to the bollards - typically a triple strand, or two triple strands (in high traffic areas, like border cities).
As part of the President's deployment of the Military to the border, in support of DHS, several hundred Combat Engineer troops are working at any given time, hardening Ports of Entry, or emplacing concertina. This deployment has been extended at least through 30 September 2020, and shows every sign of being extended for the next fiscal year, just as it was this last.
They emplace concertina at a rate of several hundred miles per year (100 miles of concertina is about 33 miles of bollards with triple strand). Initially, the Military was outpacing the construction of new bollards, but no longer. The pace of bollard construction is now about 5 miles per week, and expected to hit a mile per day average, by the end of the month.
An unprecedented mountain of money (over $12 billion) has been identified to put on contract this year, and the new awards and mods to previous contracts are already starting to drop. It is unlikely that the Military concertina effort will keep up with the bollard construction this year or next, but they will continue hitting the priority areas first.
The incremental cost of adding concertina is low enough, that local Border Patrol Commands can finance it if push comes to shove, or in the future, after the Trump Program is complete. Potentially, a temporarily increased Military deployment, and/or an additional commercial contract might be added at some point, to catch up with the rapidly accelerating deployment of new Wall System.
A tangle of concertina, 30 feet in the air (about the height of a fourth floor window sill) is a seriously life-threatening obstacle. Even the 18 footers instill a significant fear of heights effect, and will produce serious injuries from falls (30 footers will kill half or more of those who fall).
Concertina very significantly deters/defeats the ladder and rope attacks, which are the main vulnerability of the bollards, for average people. Even without concertina, the complete "wall System" package of bollards, response roads, lights, cameras, sensors and alarms are very effective. They are in fact designed to achieve full operational control of the border where they are installed.
Concertina is a useful, low cost and low maintenance enhancement for topping bollards. After the anti-climb plate (to deter/defeat free climbers without equipment), concertina is the next most import obstacle enhancement (for ladder/rope attacks).
In the past, border barrier has been heightened by welding extra material on top. 18 footers are pretty tall in real life though, when you are looking up at them - much taller than the 8 foot landing mat that got extra sheet metal added on top previously. I think we will find that they are up the job, in all but the very most intense segments of the border.
Even in some of the more intensely challenged segments, like within the Nogales, Arizona City limits, 18 footers have proven effective, with almost 20 years of experience there.
Nogales' pre-existing 18 foot bollard barrier, receiving a concertina upgrade, around January 2019:
