Honestly, the wine cork trick doesn't sit right with me. They're too soft and can compress or rot, defeating the purpose of lifting the pots. I've had much better luck with those little plastic pot risers you can get at any garden center. They're cheap, designed for this, and won't decompose like organic materials. Plus, they keep the air flowing evenly under the pot, which corks might block. Have you tried anything more durable, or were corks just what you had on hand?