>I would like to set up my 29 gallon tank with one large ornamental
>decoration and no gravel and no plants.
The problem with a "no gravel" tank is that you will see every single piece of dirt (mulm) that falls to the bottom and every time a fish (or your net or your hand or whatever) goes near the bottom the mulm will swirl upwards and settle slowly.
I sounds like you have some pretty specific aquarium design goals (more power to you I say) but you may be setting yourself up for a pretty rigorous bottom cleaning schedule.
pZ -- Paul Cezanne
Please visit http://www.customline.com/peace/
and think about what is there.