There is certainly nothing stopping a major from entering to buy shares on the open market UNTIL they reach a certain percentage of ownership. Once that happens the shareholder protection kicks in and makes it far too expensive for the major.

We're probably fairly well protected from a major being able to purchase control on the open market. I don't mind if they buy 20% of outstanding shares on the open market since that would drive the price WAY up and allow some people to take some profits.