traditionally marzipan is put on top of the cake. to get the marzipan to stick to the cake, i melt guava jam, (the clearer the jam the better) and brush a layer of the jam on the cake. roll out the marzipan the same way you would the fondant. apply to cake. leave to dry a little bit. roll out fondant, brush marzipan with white rum or clear alcohal, (not a lot) then apply fondant. trim and decorate as usual.