Well from other posts I have been told that it can shoot off into the distance and rub up against a wall, so you should always check the entire area out. As for the rarity, I would say it is about the same as any other rare so in the <5-10% rarity. Of course, you could farm Pete and have the chance of him dropping it (which happened to me plenty), but if you lack the DLC then that may be a problem. But keep grinding! It is a pretty great shield for tank builds.
Xbox Live Gamertag - Devildude720 Sorry if I abruptly stop responding to posts, I have the attention-span of a banana.