That should be fine. He describes what he wants, leaving out its intended use. Let them think he plans gruesome torture. It's the natural thing to think, when Eternal Winter asks you to build a sort of little open cage with a strong metal spike through the middle, never mentioning that the measurements he requests and the unusual design of the lock are all so that he will be able to lock it in place with the spike through his own heart. Perhaps that will be suitably permanent.