Where in the discretion of the commissioners it is desirable, they are hereby authorized to make contracts of insurance with any insurance company authorized to transact business within the state providing for insurance against loss by fire, and against any and all hazards on any or all property belonging to the county, including insurance to cover liability for damages to property and for bodily injury arising as a result of the ownership, operation or use of county vehicles. In consideration of the premium at which any such policy shall be written, it shall be a part of the policy contract between the county and the insurance company that the insurance company shall not be entitled to the defense of governmental immunity of the insured. Immunity of the county, against liability damages, is hereby waived to the extent of the liability insurance carried by the county on such vehicles. Nothing herein contained shall be construed to require the making of such contracts of insurance by the commissioners on behalf of the county; provided that the board may create or participate in a self-insured risk program.