daf bit: Bava Metzia 80

[cellio]

The mishna says: if a man hires a team (cow + plow + handlers) to plow on the mountain and he instead plows on the plain, and the coulter breaks, he is not liable. However, if he hired to plow on the plain and he plows on the mountain, he is liable for damage because those are harder conditions. The g'mara then asks: in the first case, where he is not liable, who is? There are two workers, one to drive the cow and one to guide the coulter, and the law is that the one who guides the coulter (which broke) is liable. But, the g'mara continues, if the place is known to abound in stony clods, both are responsible. (80a)

The g'mara doesn't consider the option that the owner, who I suspect is not one of the workers, just has to accept it as a cost of doing business. The worker, not the owner, is apparently responsible for inspecting the tools before starting the job. (The reason I suspect the owner isn't one of the workers is that in some other places where a borrower would otherwise be liable for something, if the owner is present he isn't -- the owner had a chance to object, take precautions, or whatever, so if he didn't he bears the liability.)