you invest in a pair of Wolford twenties? Someone recommended them to me on here a week or so ago (sorry can't remember who, but thank you :) ). They don't sag or bag anywhere. They are a micro-net so they are far more flattering than regular fishnets and give your legs a lovely silhouette. John Lewis had a special offer with 20% off so they were £16 instead of £20. Not sure how long that lasts for though.