I suggest that everyone read this report:
It was written by two military experts who have significant experience. The report seems long, but one can get the meat of it on pages 9-15.
Note the recommendations.
In addition, it is interesting to search the word “fence” in this report. A fence is not the magic bullet in any portion of this report.
I note with interest that a "fencing the river" is not mentioned among the recommendations. It apparently didn't even bear consideration.
Blocking off access to water to a semi-arid area -- and essentially leaving the country on the other side of the border with unimpeded access and de facto possession of the river -- makes no sense whatsoever.
On the other hand, enhanced communications and intelligence collection, technology and armed outposts make all the sense in the world.