Albert Barnes Commentary Job 39:11

"Wilt thou trust him, because his strength is great? Or wilt thou leave to him thy labor?" — Job 39:11 (ASV)

Will you trust him?—As you do the ox. Great confidence is necessarily placed in domestic animals, and reliance on the fidelity of the ox and the horse is not usually misplaced. The idea here is that the unicorn could not be so tamed that important interests could be safely entrusted to him.

Because his strength is great?—Will you consider his strength as a reason why important interests might be entrusted to him? The strength of the ox, the camel, the horse, and the elephant was a reason why their aid was sought by man to do what he himself could not do. The idea is that man could not make use of the same reason for employing the rhinoceros.

Will you leave your labor to him?—Or, rather, the fruits of your labor—the harvest.