Now here's an example of what a good idea is-
Sticky foam is back, defending nuclear weapon stockpiles.
Some facilities storing uranium and plutonium now boast steel doors with containers of hydrocarbon solution built into them. Breach the door, and the liquid comes foaming out under high pressure, expanding in bulk by a factor of forty and sealing the breach with an impassable obstacle.
The idea is that sticky foam will delay any attackers for long enough for the defenders to call in reinforcements. Experiments with explosives found it was impossible to break through the doors without the foam barrier deploying. Another test showed how a defender could release the foam by shooting it with an M-16.
This I like- simple and effective.