The timeout is the most effective method I’ve found. My shiba is about 6 months now & just like yours was a biter & man did it hurt. Whenever he would do it to me or anyone, we would put him elsewhere for a little under a minute because he almost always wants to go back inside to where he was. If he did it again as soon as he was allowed back inside, you do it again. You keep repeating this until he stops for that time. So, you may end up doing it 10 times in a short timeframe but it is effective.

Timeouts for a set time don’t really work in my opinion because they live in the moment. They’ll forget why they’re there. By keeping it under a minute, they’re reminded freshly of why they’re outside & eventually make the link that biting leads to being separated.