After removing the worn fabric covers from your outdoor furniture cushions and pillows, use some inexpensive plastic shower curtains liners to make some waterproof covers. Cover the cushion foam or polyfill with the plastic covers before covering with new fabric. This will prolong the life of your foam or polyfill cushions and reduce mildew. Make sure to use thread that is intended for outdoor projects. Get some new fabric specially treated for outdoor use and make some new cushion covers. There are a number of beautiful styles of outdoor fabric available today. Look for deals on outdoor fabric during the fall months. Add a zipper or velcro to the new fabric covers so that they can be removed for easy cleaning and storage.
A helpful tip: To keep squirrels and possums from destroying your outdoor upholstery, spray the cushions with a mixture of ammonia and water. I don't have an exact measurement on this but I would imagine it would have to be a pretty small amount of ammonia. I've also heard that putting a rubber snake on or in close proximity to your outdoor furniture will help deter varmints.