We tried tonic water, bananas and a few other things. We have now had a bar of Dial soap under the sheets and near the middle of the bed for 6-7 years now. I didn't tell when first putting it under the sheets but it worked anyway. I have wondered about putting a new bar in after all this time, but it's working so I guess we'll leave it be. Who cares why it works, as long as it does.