OK here's something thats gonna help.... Use the sinker in the pic below! It's amazing, but the plastic extensions actually hold the sinker up off the rock, making it difficult for the sinker to actually become stuck in a crack/crevice... You're still going to lose the odd bit of tackle, but it's going to improve it drastically. And, when the sinker does become stuck, it usually catches by one of the plastic arms... all you do is pull hard, the plastic arm bends, and then you reel in quickly... When using these plastic grapnel sinkers on rocks, you gotta retrieve quickly, otherwise you're asking for shtogh.
Use it, don't use it.