So, you can go for these routes:
- No derivative works, you just say "please don't use my stuff, k thanks" and during the second jam any submission that try to break this will be removed.
- You allow derivate works, but you better use one the license you can find here to specify the restrictions on the work that you have to respect to make use of the work.
- You are open for collaboration, so others can work on your work but you have to be part of the team.