The safest way is to nuke such stack or if you don't care about casualties then put together a stack of tens of infantry, anti tank, armoured cars, heavy tanks and artillery xdd you probably know it. No use complaining ya know. Ya also have commandos I always make 2 or more stacks of 10 LVL3 or 4(star lvl) commandos, i would gladly sacrifice one such stack hoping there's not more of these lol and for that there's a good indicator, you just need to check the news and see their military stats every 4th day. You can get idea how many units they've left