Rock Slide/Stone Edge provides more coverage and than Gyro Ball (And Stone Edge has just as much power with STAB factored in.) And why not just have a Tyranitar/Hippowdon on your team to set up Sand? It boosts Shuckle's Sp. Def astronomically (In the 700's with no investments) and will help Excadrill without having to rely on Shuckle. That also frees up Shuckle for another move, such as Toxic to help stall out the opponent.