Is there a way to force a footer which refers visitors back to my hosting company which can be auto embedded on sites I host for free or at most a small banner ad at the bottom?
As far as I’m aware and believe, if the client has full access to host files for their domain, I don’t think it is possibl, as it could be overwritten.
I’m not too sure of legalities, but you could add required as you want but I would most likely have it in your T&C that they must display your back link as you want or pay for hosting and have it advert free.
I’m sorry, I could be wrong but I’m thinking you may have already considered this.
I didn’t think there was anything, but wanted to see just in case.