I believe your idea of creating a community mural/graffiti wall in order to prevent and eradicate the graffiti problem is a good choice. While I believe friendship is a good theme, I don't think it pertains to this subject very much. Maybe we could get creative with it and base it off a song or work of art that's meaning has to do with the communities relationship. Such song could be "Come Together" by the Beatles or "Strawberry Fields," another classic by the Beatles. The painting could be quite literally a strawberry field with friends laying in it or a image of many different people "coming together."
The wall could be a very colorful painting in order to 1. draw attention to the club and 2. prevent graffiti artists to paint on it considering that their work would not be noticeable. We, as a unified club, could approach the government about this and the message it would spread in hopes of having it be government paid. We could also talk to high donaters in the club and ask if they would like to help.
I hope I provided a few ideas as to how to solve this growing issue, I am excited to see where this project leads, (y/n)
