Place your flowerpot onto the saucer. Flower pots have a hole in the bottom, so to avoid having the sand pour out, place a saucer under the pot and keep it there during cooking. Fortunately, the saucer will remain cool no matter how hot the pot becomes, If you need to handle or lift the pot, do so only by the saucer but, please be very careful.
Fill the pot nearly half full with sand. The sand insulates the bottom of the pot from the heat so you can set your flowerpot grill on surfaces and it won't transfer the heat. Of course, you need to keep flammable materials far away from your flower pot grills.