I use sodium hydroxide in both my rock area and underneath pavers. It doesn't leach too far into the surrounding soil, but goes far enough to effectively make it a caustic wasteland for anything wanting to grow there for years. What is great is if you need to clean the area up, just some water and mixing will cause the lye to react and dilute.
The Biden Admin obviously can't give any weight to the idea. If they so much as entertain the legitimacy of those rumors at all then they've already basically conceded.
It's a damned if you do, damned if you don't position for them at this point but from an optics POV it's better to just keep lying and denying until something official actually takes place.