I taught on a small island in Alaska, where they tried to pull this, for 2 years no less ! It is bogus, you don't find it in professions (dentists,doctors,etc) and it undermines fair play. If you need to be the," only game in town," you have a problem. Clients should come to you because of what you offer, not because you shut-out other talent. Believe in your own abilities and school; then let your collegues teach in gyms, their own shools, rec. centers of whatever. Take the higher ground. Jen.