Larry Hastings uses Cog, but worries about missing new files that need to be Cog'ged. To solve the problem, he wrote Nocog. As he describes it, "Nocog scans over its input files, and if any of them contain Cog code, it prints an error and returns -1. If none of them contain any Cog code, it prints nothing and returns 0."
This isn't a problem I've encountered, but I understand the impulse: the more that code can detect its own problems, the fewer problems will persist. This applies even to builds.