Ah, well that last bit certainly nudges me a little harder towards OO, which is where I was leaning anyway, eventually ...

In the short term Hash::Util::lock_ref_keys keeps me from looking for typos at run time, which was what I wanted ... initially ...

Thanks again for all your input. Incredibly helpful, and enlightening, and oh-my-god-do-I-have-a-lot-to-learn!