Can a private business owner fire a marketing consultant who's marketing plan lost money and produced no sales after a 100,000 dollar investment?

Is there a contract which limits the reasons why the consultant can be fired or provides that he/she/it will be a consultant for a defined period of time?  Is the consultant being fired for some reason which is barred by statute, such as race, religion, etc.?  If not, the consultant can be fired at any time.