If even the terrorists in the Caucasus with much less help, much less equipment, and without the intel and recon capabilities of NATO behind them could pull off stunts like this what makes you expect that Ukraine cannot? At some point you just have to be realistic and not expect the Russian armed forces to perform miracles. The correct response is what matters when perfect prevention is not possible. As for what the Russian media claims, a lot of it is sensationalist. After all, they have an interest in generating controversy and getting clicks/viewers. Picking up on the smallest oversights or mistakes and exaggerating them into big blunders creates outrage, which is good for ratings and is to be expected.

Anyway, it is virtually impossible even with modern technology to completely prevent all physical penetration of front lines that are this long. What deters the enemy is the certainty of failure and massive casualties. If someone is truly suicidal they will always find ways to cause chaos and do harm, but at least they can only do so once. In situations when they are desperate for a morale boost the Ukrainian leadership may be willing to make such sacrifices, but this is not a viable long term strategy, performing PR stunts to “humiliate” Russia and harm a few civilians at the cost of precious equipment and trained manpower that they are already struggling to replace.

The main job of the Russian military is to defeat the enemy. These sorts of actions by the Ukrainians are ultimately self-defeating. They are also not exactly swimming in munitions at this point and as horrible and cynical as it sounds, in the military calculus every shell expended on civilian targets is one less shell used to degrade the opponent’s military potential, to attack or defend against the actual enemy army. Terrorism is simply counterproductive, it may be politically beneficial for Ukraine and embarrassing for Russia, but militarily it is useless, provided it does not provoke the enemy into doing something stupid.