It would help if you gave a little more information about your business and your target market. With regard to employees or independent contractors stealing business, a client is going to go where they want to go.
However, to protect your business, you may want to look into a non-solicitation agreement rather than (or in addition to) a non-compete. The fitness industry is very competitive but many trainers do work in multiple locations (I have my own in-home business, but also train and teach at other facilities–we do have a level of trust and many times we refer work to each other). A non-compete agreement is too rigid in my opinion and may hinder your efforts to find quality trainers. I would never sign a non-compete personally.
Good luck and if you have a chance to update your profile it will give us more information.