The Russians are already using land mines in certain areas of the Crimea and even north of the isthmus. That was reported by my brother-in-law who live in Alushta on the Crimean coast but get reports from his contacts elsewhere.
No surprise there, Russia is where Putin puts his army. His army is in Crimea and nobody is about to push them out of there.
Russian combat engineers were seen placing mines in the land bridge connecting the peninsula to the mainland in order to foil any Ukrainian attempt to retake Crimea, reports Haaretz.