I certainly appreciate your desire to protect your knowledge. One of the risks of opening up your operation to outsiders is that they will learn some or all of your secrets. Once a person has learned something, it is impossible to get it out of their head.
But telling an employee that if things don`t work out at your company, he or she must pack up and move out of town in order to work at their chosen profession strikes many people as unreasonable. If this was a highly compensated sales or executive position you might be able to make a case for it, but trying to place such a restriction on the average working person (such as a designer) will be tough.
It`s hard to imagine a good candidate being willing to accept these conditions unless you were paying two or three times market rate. I think you may end up with people who are desparate for a job, or people who are willing to sign anything because they have no intention of honoring the agreement anyway.
I`m sure that your attorney knows more about this than I do, so please listen to him or her and not me.
Michael A. Silva