Point defense such as you are describing is almost impossible to successfully implement, and can easily be overwhelmed. The Israelis do it, but they have no illusions that it will stop a determined enemy.
Their philosphy is one of concentric defense, with defense at the point of attack being the last resort. They much prefer eliminating the threat, early and as far away from the terrorists’ target as possible.
They go after the planners, the financiers, the recruiters, the indoctrinators, the keepers, the inspirational and operational infrastructure of the terrorist organization whenever possible. To try and stop them once they’ve reached the target is to fail 90% of the time.
A (retired) Mossad agent told a group of us once, “You have people who need killing, and you must kill them. You Americans have not yet learned this lesson. But unfortunately, you will.”