Thank you for you time and inquiry. To stop the furniture from scathing and moving on the deck I would suggest using Rubber Furniture Pads. These protective pads can be placed under the legs of your patio furniture. They can also be found online.

This should do the trick for you. You will want to stay away from the felt ones as the felt will not hold up in an exterior application. But the Rubber or even vinyl ones will work just fine. I hope this helps please let me know if there is anything else that I can do for you.

We always tell people to use pet safe ice melt as it is a little less abrasive than rock salt.