He's a brand new CEO. I just alerted him that bidding before asking isn't best practice.
Otherwise you have two options. Under your main "Settings" you can 'block ceos' or something like that. That will prevent any bids, but will also prevent any ceos from building in your country.
The other option is to "nationalize" the state-corp you don't want anyone bidding on. This protects it, but leaves the country open to new investment. Only problem, you can only nationalize up to 25 state corps.... so nationalize your most cherished corps, at least until their value is above 1T. If someone bids on one of your state-corps and is willing to pay you more than a trillion for it... let them!