The ANO is a law, so that requirement is law. How you do it is up to you; you could argue that if the owner has given you carte blanche to operate at will, then that constitutes notification.
I'm sure I saw somewhere, though, a requirement for aerodrome operators to keep some kind of record, hence the prevalence of signing in/out books at small farm strips with a caravan. I'll have to have a dig. Where's Bookworm when we need him?
Tim