How many ways are there to "watch" for such events and combine all source intel to see where the rats scurried off to seeking a hiding spot afterwards and deal with them as has been going on with the Hamas, Hezbollah, and Iranian Guards of late?
They also have to move the weapons about and set them up prior to launch which also affords some opportunities to be found out.
Remember the Iraqi use of Scud missiles and what resources were devoted to dealing with them.
It is not easy, the area is large, ground forces would have a hard time operating there without being compromised.
When several Big Brothers start snooping it gets hard to hide and a few mistakes can become quite injurious to one's health and well being.