1) Suppress metagaming, especially such harsh and power-gaming-oriented metagaming.
2) If you introduce the laws of physics, follow them to the end. Someone who is not knowledgeable about the laws of physics came up with a "clever plan"? It's their problem that they blew themselves up with their own magic!
P.S. Liz, we were just discussing the situation in one chat. I sarcastically said something about playing along. I'm afraid the sarcasm wasn't very noticeable, I apologize.