Also, as a contractor, they must be allowed to work for other companies. They may choose to only work for you, but if you were ever audited, this is one of the things they look for. A non-compete clause is a red flag for a tax auditor and not enforceable in many states.
Does anyone know if an independent contractor can work in your office without confusing independent contractor relationship?
http://www.beckreedriden.com/wp-content/uploads/2010/12/Noncompetes-50-State-Survey-Chart-12-12-2010.pdf