As I said before, I love the sound of the obsolete Marxophone, but they're expensive on ebay.  I made this guitar-marxophone with hex nuts glued to street-sweeper bristles stapled to a chunk of wood.  The marxotar straps to the guitar's tailpiece and strap button with zipties, and can be attached and  removed without any damage to the guitar.

Despite my unpracticed fumbling with the  guitar marxophone and Open D tuning, I think this thing has a lot of promise.  Hey manufacturers!  You can have the idea, but I want credit and some free product!  (Actually, I wouldn't be surprised if someone else has already had the same idea.)