How does this sound for an exclusivity clause?

I am doing a small festival in the fall, and they have agreed to make me the exclusie face painter. Tey don't have an exclusivity clause in thier contract so she asked me to just add it to the contract before I sign it. This is what I am plannign to add:

*Face Painting by Pam will have exclusive rights to face painting at this event and if any other vendor and/or attendee offers face painting either for a fee or as a free service, they will be shut down immediately.

How does this sound? Is there anything else you think I should say?

Thanks!