I'm using the nice earth theme Justin S made and I dont want users to change it, but I dont see an option to prevent it. So is the only way to prevent this to delete the "default" theme (the one that comes with 1.6) ?
In the settings for each theme there's an option for what usergroups can view the theme; if you edit this on all themes and only give them the ability to use one of them, that's all they'll be able to use