I didn't go looking for fangbeasts anywhere else since I got enough from chopping rocks. I do get dire boars but I figure the energy used to defeat boars will be less than collecting 50 cows to get a fangbeast. I'm pretty much done, but I did get quite a few masks from adventures. My troll camp's drop rate was close to 50%. I believe that 50% is programmed in the system, if you're getting a lower drop rate it's likely to improve so hang in there