As of this morning, I've ridden Lance three times in the arena. We review proper Mr. Manners behavior before starting, then we walk for up to 30 minutes. I let Lanc stretch in between making him march, accept contact, leg-yield, halt, rein back, and pivot on his front and hindquarters. He has been very good, and has a nice, foamy mouth during each ride – something he didn't get on our road/field rides.
We will ride out and about again soon. I am confident last week's bad behavior was a temporary lapse in Lance's "new world order." He didn't not learn R.E.S.P.E.C.T. from his breeder; when he doesn't get regular reminders it is easy for him to revert.