The bitter apple stuff is a rather vague aversive, in that its aversive the whole time the dog can smell/taste it (so before they chew/bite something, and long after the fact) - aversives only work if they're very accurately timed with the unwanted behaviour (whether you're pro using them or not, thems the facts).
The behaviour is a symptom... of his overwhelm, boredom, high arousal, frustration - take your pick, he's probably got them all. So in the broader scheme of things, try to reduce those things.
On a practical level - mm, a chain lead, possibly with a slip cover over it if theres any risk of him getting a tooth caught in it..
If you're using a harness with two points of contact, you can use two leads - downside is it gives you more to juggle, but you then have the option of dropping one, which gives him nothing to tug back against.
I think I'd go with a chain lead, and with a tug toy to offer him when he feels like he's needing to bite/tug. (Probaby a long tug something furry on the end rather than the Puller rings for playing tug games at home).
I'd also consider upgrading harness if he doesn't have an escape proof harness (Haqihana, Rabbit Goo, there are others er.. Ruffwear do one) that has the second belly strap further back, stops them reversing out, which pointy shaped dogs can do so very much more easily than other shaped dogs.