Other clever ideas
I forget what the code name for the concept was--might have been "porcupine"--but somebody came up with an idea to protect missile silo farms from first strikes. Set up sharp steel rods, a few feet apart, and carpet the entire area with them. Make them as tall as you can get away with.
Any burrowing warhead--pretty much a requirement for taking out a properly-designed missile silo--would be destroyed by these things on impact.
Obviously of no use against city killers or air bursts.