Ukraine can use landmines to halt Russia

It takes two to tango, and the Russians have been mining for the same reason anyway. Once Ukrainian troops are safely outside the range of Russian artillery, they can focus on air defense. Any Russian troops who make it through the minefields will have a hell of a time advancing or retreating into their own minefields. 

GATOR mine system - Wikipedia

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The GATOR mine system is a United States military system of air-dropped anti-tank and anti-personnel mines developed in the 1980s to be compatible with existing cluster dispensers. It is used with two dispenser systems—the Navy 230 kg (500 lb) CBU-78/B and the Air Force 450 kg (1,000 lb) CBU-89/B. Additionally the mines are used with the land- and helicopter-based Volcano mine system.

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Volcano mine system - Wikipedia

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The M136 Volcano Vehicle-Launched Scatterable Mine System is an automated mine delivery system developed by the United States Army in the 1980s. The system uses prepackaged mine canisters which contain multiple anti-personnel (AP) and/or anti-tank (AT) mines which are dispersed over a wide area when ejected from the canister. The system, commonly referred to as Volcano, is also used by other armies around the world.[1]

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Thoroughly mine the whole front line then pull back 5 km. If the Russians are dumb enough to advance, they'll have to deal with landmines and Ukrainian artillery simultaneously. 

I like Russia, but they are in the wrong in this war.