Good question. I don't think there is any surefire method of sheltering yourself, otherwise, unscrupulous manufacturers would be taking advantage of it. Not only do we want protection, but we also want to sue others who are negligent in making their products.
You should really talk it over with a lawyer. You might have to give title to your main assets to someone who won't put you out on the street....oh ya, your wife
Perhaps form a limited company with only yourself as the director. You'll have to risk whatever assets you and your company owns to back your products.
Getting liability insurance is not too difficult, at least until the first court case.
You must do your utmost to make the widget as good as you can, with quality control and testing to ensure that the "dangerous part" is as well made and as safe as can be reasonably expected. You might also hire an outside engineer to give some kind of an idea of whether your design is good. Most likely, none of them would be willing to go on the hook for you either.