[mseebach]

Do you want to see what happens if you slip a big knife into someones carry-on? It's harder than "covertly dabbing" someone, but not impossible. On the other hand, big knifes are substantially easier to get your hands on without drawing attention to yourself than even microscopic amounts of Semtex. Yet, it doesn't happen, so I think we're safe here.

[chopin]

Just use fertilizer. I am pretty sure that will work, too. If not, congratulations, you know now how to defeat the guard.

[mseebach]

The system would need to be resilient to small amounts of fertiliser, otherwise it would trigger on anybody who's been on a farm or done gardening recently. Heck, I use fertiliser when watering plants in my flat. That's not a practical level of false positives.