Make sure your professional photography insurance policy covers equipment in your "care, custody, and control". Some policies include this. Others exclude. And others, offer an optional endorsement (rider).
When renting a lens or camera, make sure and rent the lens in the same entity name that is listed on your insurance policy. For example, if your professional photography insurance policy lists your company - "ABC Photography, LLC" or "ABC Photography, Inc." as the named insured, make sure the rental agreement you sign with the rental company matches. If your policies names you, a sole proprietor "John Smith", then rent the equipment in your name "John Smith". I have never seen a claim of theft or damage to rental equipment denied for this reason; however, the insurance company could deny coverage because "insurable interest" does not exist. Meaning, if one entity takes out an insurance policy and another entity rents a lens there is no insurable interest.