At 10 wks of age, distraction is key! If it were me, I would keep him occupied and engaged with me while outside, and bring him in when he starts losing interest. Barking at stuff is self-rewarding, so simply ignoring him might get the message across eventually, but it may not as well. From my perspective you'd be better off keeping him engaged with you, leading him to do stuff that's even more fun, and containing him where he doesn't have stuff to bark at otherwise. He'll likely grow out of this excessive barking phase, the key is structuring his environment such that it doesn't become a habit.
It's not the size of the dog in the fight, it's the size of the fight in the dog. Mark Twain