As some of you may already know, I manage a website and app for a small music festival. It runs on a shoestring budget and helps to support the village I grew up in, so I volunteer my time and resources. Part of this is creating the site and things like posters using resources that I've made.

Recently we had an issue where someone created a logo for us, and after we'd used it for a few years, they claimed it back. It turned out that when they created the logo, neither side thought to draw up any sort of agreement on how it could be used. I want to put something in place that makes it clear that anything that I create for the festival can be used by them forever, but without restricting myself from using it.

My main concern is for the website and app, so that I can use the same structure in the future.

I'm not concerned about the fine print, like saying that I can use this specific text layout or whatever, I just want to stop either side from restricting the other in the event of a major falling out, with the exception of things that are exclusive to one side or the other, like the name of the festival.

What would be the best licence for that please? Thanks in advance :)