I recently started doing decorated cake boards with fabric. I have covered the fabric with half a two gallon bag to greaseproof it and it has worked well. Last week I was delivering a 10" round cake and the cake slid on the board! Luckily it only smooshed a tiny part and the customer could have cared less. So I was wondering, has this happened to anyone else? Would I be better off using press n' seal? I just like the nice clear look with the bag.

do you put icing on the board to "glue" the cake to the board. Was this a single tier cake?

Yep, that can happen. Whenever I fear the cake may have a sliding issue (for instance, I traveled 4 hours last weekend with just an "ordinary" [ decorated but only 1 cake, no stacking involved] and I did not want to have to worry about the cake sliding on the board as I was driving 75 MPH on the highway) I put 2 small dowels through the cake and into the board. My board was covered in fondant...with fabric and plastic that is going to be a bit more difficult. Was there a cake board under the cake? If so, maybe next time you could use a little glue or tape between the board and plastic bag. If it will not come in contact with the cake that might be the best way to go.