You can't.

Your percoset example is a perfect reason why. How do you suppose those pills get to your 7 yr old once they place the order?

Either via mail or by delivery, right?

If by mail, you're gonna notice when the unexpected box arrives and you open it up and see what's in it.

If by delivery, you're not gonna know. Your "relatively safe cul-de-sac" has regular deliveries of black market items because the drug trade has gone mobile.

Drug dealers often engage in other sales of illegal products and they being an element in that is interested in buying those things.

There is nowhere safe anymore. Not really. It's just more hidden in some places to maintain a certain aesthetic.