Answer from past - we used SOUND to soft stones.

October 9, 2019 
Just some speculations about what i have seen in Saint-Petersburg.
https://www.google.ru/maps/place/Solyanoy+Pereulok,+15,+Sankt-Peterburg,+191028/@59.9429589,30.3414963,3a,75y,268.53h,90t/data=!3m7!1e1!3m5!1sZMbVQPsLw_sZ8qoATxFMiw!2e0!6s%2F%2Fgeo0.ggpht.com%2Fcbk%3Fpanoid%3DZMbVQPsLw_sZ8qoATxFMiw%26output%3Dthumbnail%26cb_client%3Dsearch.gws-prod%2Fmaps%2Flocal-details-getcard.gps%26thumb%3D2%26w%3D86%26h%3D86%26yaw%3D268.53235%26pitch%3D0%26thumbfov%3D100!7i13312!8i6656!4m13!1m7!3m6!1s0x4696310b4377a3dd:0x1de1c6381304fd96!2sSolyanoy+Pereulok,+15,+Sankt-Peterburg,+191028!3b1!8m2!3d59.942946!4d30.3405309!3m4!1s0x4696310b4377a3dd:0x1de1c6381304fd96!8m2!3d59.942946!4d30.3405309?entry=yt

Original video on youtube channel 'Global Vision' - https://www.youtube.com/watch?v=GMWx25ZVcsQ

Telegram channels: https://t.me/anti_swarm
https://t.me/Celno3or
https://t.me/videoCelnozor

'GlobalVision' on rumble in russian - https://rumble.com/user/Celnozor