My youngest grandson - a little 4x4 enthusiast who loves driving on rocks with 4x4 vehicles with his dad ("klippe ry" as he says in Afrikaans).
So at 3 years old he wanted a birthday cake with rocks......... everything except the vehicles are edible as I could not see myself making them.
He loved the cake and being able to drive his 4x4 vehicles on the rocks.
I knew the little man was going to be very upset when we wanted to cut the cake, so therfor made the top part of the cake a dummy cake. This was then removed and he could continue driving his vehicles on the 4x4 track.