The field guide · rule 09 of 16
Several simple guards beat one clever wall
No single check is perfect, so stack simple, separate guards. When one misses, the next one catches it.
What it means
Every check has gaps. Instead of one clever defence, stack several simple ones that work separately from each other. If one fails, the next one catches the problem.
What goes wrong without it
One spam filter fails, and fake sign-ups flood the system overnight.
How I build it
- The Space.ke site stops spam with a hidden trap field, a limit for each visitor, a robot check on sign-up and a check on where each request comes from.
- My AI agent system removes private data twice: once when an agent reads a record, and again just before any text is sent to an AI service. If the cleaning fails, nothing is sent.
- Business rules are checked in the code and again in the database, so a script that skips the code still meets the rule.
Ask your team
- If your main check failed, what would catch the problem next?
- Are your most important rules also enforced in the database?
- Is private data removed before it leaves your system?
How a review checks this
For each serious risk, a review counts the separate guards in its way, and flags any risk that has only one.
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