most non disclosure agreements relate to the technology or process. You are looking for a non compete agreement. Those are usually structured to encompass a specific geographic area and are valid for certain amount of time. Indefinite or very large areas are very hard to enforce in court.
you will have to specify the amount of time they are not allowed to go after the other company. Generally, anything over three years is probably not going to hold water (your customer might find the other printer on their own and they have te have the option of going to them if they are not happy with your services, so courts generally think it reasonable to impose the few years but not much longer than that as the likelihood of the customer staying with you past that time period diminishes).
If you think that is long enough, then just write something up in very simple language stating that if you present the idea he is not allowed to pursue that customer for the specified time and is not allowed to disclose the details of the working relationship pertaining to this particular project. From what I understand, if you do not contact an attorney, courts are more lenient in the interpretation of the language and the general spirit of the agreement takes precedence over the specific wording.
pierre
