Comment by ralferoo

Yeah, I have all my _acme_challenge as their own zone so that BIND can auto increment the serial number without going through the pain of locking/unlocking the entire domain and hoping you don't end up with stale data that stops syncing.

That said, I like that the current system proves that you have control of the domain at the time of renewal, and I'm not sure how setting a one-off token would achieve the same.