Iceland has an interesting mechanism related to this. Some driveways have a gate with one vertical post on each side, and three removable horizontal beams. If the beams are moved aside, you may enter. If all three beams are hung in place, you must not enter. If two beams are up, you should seek permission to enter. That's how I remember it, anyway.

The point being, yes, you do need a lock or some mechanism to say "outsiders should stop here." You need this for two reasons: first so that honest people know where they are not welcome, and second so that dishonest people can be shown clearly to have broken a social contract.