I wonder what the local zoning commission has to say about the guy building a personal toxic metal death ray in his backyard?

That is why I will never live in a HOA neighborhood.

The zoning commission runs at the town/country level, so even if you don't have HOA busybodies you still need to get the permits. The law is usually worded such that if you're doing something abnormal you don't get a "there is no rule that says a dog can't play baseball" loophole, you instead have to bring it up before the county council and justify the project.