Re-post of link from another anon several breads back.

I liked the part about using foam to temporarily block a tunnel. Shows they see value in preserving some of them, as well as preventing damage above in urban areas.

I have a suggestion for the military types, if they haven't already gone this direction-

Foam is sometimes doped with capsaicin to keep wildlife from messing with it.

Could work great for this application. Make a plug 20 feet long full of pepper foam!

https://www.realcleardefense.com/articles/2019/07/03/the_army_is_preparing_to_go_underground_114555.html#:~:text=The Army is spending %24572,combat brigades for subterranean operations