How to protect rear derailleur while mountain biking? I am a college students, and I live right next to an amazing rocky area (picture below), I bike every day, and while I am getting much better and more confident I still take a pretty hard fall every so often.  

My derailleur has been crushed so many times, and I have been forced to literally pull on it to bend it back into shape on more than one occasion.

I am hoping to replace the derailleur soon, but I would like to know if there is a good way to protect the derailleur during a fall - this will decide how much I spend on a new one!

This is the stuff that is crushing my derailleur every time I fall.
They make bash guards for derailleurs which mount to the frame which protect a derailleur in a crash like 



but these are dangerous in that they transmit a hit to the derailleur to the frame (and frame damage is typically less repairable/ more expensive than a derailleur damage).

Usually, what gets damaged in a crash is the derailleur hanger, which can be bent back into shape with a special tool at your bike shop (Park Tool DAG-2 for example). You should never pull the derailleur into shape by the cage (this is the weakest part of the derailleur and can damage it more). On non-steel bikes, this is often a little replaceable part which is designed to deform in a crash so hopefully your derailleur makes it out alright as does your frame (so if you can't bend it back into shape, you can replace it). 

Typically the Shimano Deore level is what gives you the best hit taking ability for the price, though it depends on how you fall and how the derailleur gets hit and stuff. The best thing to do is "don't fall". But obviously, compatibility within brands and budget dictate what to buy. 

I'm curious as to how the derailleur is "bent", and how you're straightening it though. It would be good if you updated your question with a diagram or picture of your "bent derailleur", along with the type of bike you're riding.