I don't think Sauron expected Saruman to ever find the Ring, or take possession of it. He just thought that the Wizard's "feeble" attempts to find the Ring would distract his enemies long enough for Sauron to attack them, and vanquish them. Saruman would just serve as a distraction, not as any real weapon.
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But Melkor also was there, and he came to the house of Fëanor, and there he slew Finwë King of the Noldor before his doors, and spilled the first blood in the Blessed Realm; for Finwë alone had not fled from the horror of the Dark.
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