Looking to bash you bike off stuff? Cinema have you covered with their super neat and strong Beta Sprocket...

"The Cinema Beta sprocket features a high-impact plastic guard, that is bolted to a super strong 8mm thick 6061-T6 aluminum sprocket. The plastic guard is fitted down into the sprocket itself, creating additional support and making this guard extremely robust. Four small bolts thread directly into the sprocket, without the need for small nuts that can easily come loose or fall out. The high-impact, low-friction plastic material will keep your chain protected, keep you from hanging up, and allow for any grind combination you can come up with." - Cinema