It's worth having a go at making your own marzipan to cover your Christmas cake, and you can experiment with adding different flavours, too.
Homemade marzipan contains raw eggs, however the amount of sugar, and lack of moisture, prevents bacteria growing when left at room temperature, so your cake should last for 1 to 2 months iced. The most important thing is that you don't scrimp on drying time - once you've covered your cake in marzipan it should be left to completely dry out, before you then cover it with icing.