Its important to carve a cold cake. Layer and fill your cake then let it sit in the fridge, preferably over night.The cake will be stable and carving it will be a breeze.
Using an icing that contains some sort of fat that solidifies in colder temperatures is just as important. Butter and chocolate are great for holding shapes and giving support to toppings like fondant or modeling chocolate.
For this cake I'm using my favorite butter based recipe, swiss meringue buttercream.