Nothing sucks worse than getting stranded out on the trail with a busted derailleur. Actually, we can think of some worse things, but it's still pretty bad. The Shimano Deore XT M773-SGS 10-speed Shadow rear derailleur though isn't going to leave you hanging. It's compatible with their 10-speed Dyna-Sys drive train, so it delivers smoother shifts, closer ratios so you'll have fewer dropped chains and a lot more riding.
Low-profile design of the Shimano XT Shadow 10-speed rear derailleur has a smaller high-gear profile than traditional derailleur designs
Ideally matched to RapidFire shifters, top normal spring design provides responsive shifting performance for trail/all-mountain riding
Sealed-bearing guide and tension pulleys for smooth gear transitions and low-maintenance performance
Optimized gear array for smoother and more efficient shifting