This might help you if you have never used a cake dummy....after you have covered it with fondant you now need to decorate it without it moving. I use a couple of different methods. I place the dummy on a piece of non-skid shelf liner or I have a foamboard round/plastic wrapped cardboard round...that I have placed about three Removable Glue Dots in a triangle pattern that will fit under the cake dummy...place the cake dummy on the round over the dots and press down...When you have finished your project just use a spatula/cake lifter under the dummy to help break the glue bond then just peel off the dots and throw them away and wash your dummy. I used to use the nail method were you take a thick piece of foamboard and cut a large round..then you take a three/four inch nail, large washer and glue...find the center of your board and mark it...use the head of the nail to poke a hole through the board...then pull the nail out...place washer on the nail, add some glue between them so that when the glue dries it is more stable then put some glue over the hole so that it will spread when you push the nail/washer all the way through. Let dry..then just place the dummy on the nail. I did use this for a while but it began to break down the styrofoam dummy after placing and removing it over and over.
Hope this helps you...because take my word for it, there is nothing like the feeling of watching your cake dummy that you have been working on fly off your turntable and land on the floor five feet away...it is at that moment you say