AI'm making a wedding cake and the bride to be wants a deep 5/6 inch look. The bottom tier is a fruit cake. Mine usually come out at 3 inch deep. I'm loath to try cooking a deeper one. Any ideas? I thought maybe staking a couple of drums and icing over or maybe stacking onto a dummy cake and icing as one. has anyone had any experience of this or have any better ideas?

How about adding another layer of marzipan to the bottom?  If you place the cake on a drum board that is the same size as your cake, put the fondant over the whole thing - you will need a lifter to place it on the cake.  This is the top tier of a wedding cake I did for our friends' daughter.  It measured just under 5 inches high - without an extra layer.  Alternatively, why don't you bake two  shorter cakes and "sandwich" them with marzipan - you can really get some height then.

Baking a 5 or 6" deep one would take like 2 days and would not be a good bake. I would just bake another, the same height as you usually do. Put a layer of marzipan on one, and dowel it. Add a cake board with the other cake on top (and dowel the top cake, obviously, since this will be the bottom tier). Marzipan as one cake. Charge her double, since she will get double the servings. If she doesn't want to pay that much, offer her a 3" fruit on top of a 3" polystyrene, and ice that as one. 

how about baking 2 fruit cakes and stacking them with a layer of marzipan between them

AThanks everyone, I think she will go for the two cakes option!