You could try introducing a biting object. It takes the redirect idea and allows the bite to still occur, just not to anyone else. Biting is a visceral response, and nothing short of a visceral outlet seems to work (at least not at first).
Unfortunately, as much as you taught him that you don’t bite, being bitten taught him that biting gets results. He already knows it hurts, because he’s been bitten, so biting him back has less value (I don’t recommend it anyway, though I know it has helped at times, it also has repercussions sometimes that you then have to solve, and so forth…). Behavioral therapists actually say that biting back reinforces the behavior far more often than stopping it. So don’t. You might get lucky, but you probably will not.
Here are some tips that may apply:
16 ways to stop biting and hitting
general discipline for toddlers question, including biting
general concepts around biting in toddlers
different reasons kids bite and how to approach each
For us, it was hitting (with Gabe). We found the most useful approach was to identify the emotion, reflect that it is a feeling you know (yourself), say how it makes you feel (so he knew we understood), and then specify what was an appropriate (and expressive) response to that feeling, and what is definitely not.
So, when Gabe hit me, I said, “You seem angry! I get angry too. When I get angry, my chest gets all tight, my face feels hot, and I just want to HIT something. But we don’t hit when we’re angry. We say, “I’m angry” and scowl (make face), or cross our arms like this (cross arms in that typical ‘angry’ stance).” He was pretty verbal at the time, but the words didn’t express enough of his outrage, for him. What he did grasp was that there were okay ways to express the feeling, and not-okay ways.
The next time he got mad at me, he crossed his arms, scowled, and then stomped his feet really hard. He watched me carefully to see if that was an okay way to react (testing his self-chosen alternative), and, luckily, I noticed what he was doing. I made a lot of approving noises about how stomping showed he was angry, and it was okay to stomp to express anger (not my favorite, but allowable, and way better than hitting!). (At this point, I plan to include that option for Brendan - giving him a choice of how to respond lets him pick something that suits him… his favorite is screaming… though I’m anticipating biting any time.)
At this age, they are desperate to communicate, and they are also starting to experience feelings that can be kind of scary. Knowing that you have the same feelings and don’t bite, but do other things that are allowed when you feel that way allows them to 1) feel safe - their emotions aren’t that scary if mom has them, too; and 2) learn the basics of social rules.
At this age, the more you talk about emotions, point out when you are feeling any particular one, and show how you express those emotions, the easier it will be for them to follow your cues. Now that they are discovering that they are individuals and not internally attached to everything else, it can be scary to feel something new and powerful, either good or bad. This is also the basis for establishing empathy (a years-long process).
Good luck. Hope the links help.