First, I'm glad that your step daughter is OK, kraigwy.
That said, I have conflicting thoughts about a Rule #5. On the one hand, if the guy doing the work had followed Rules #1-#4, he wouldn't need Rule #5. And I agree that fewer rules are easier for most folks to follow than many. On the other, making the workshop an ammo-free zone would seem like a good idea.
I'm a lawyer, but I'm not your lawyer. If you need some honest-to-goodness legal advice, go buy some.