and until you have total control of him he should be muzzled and on a lead in public. sounds harsh i know but its better than being reported under the dangerous dogs act. your dog could be destroyed.

also try not to pick him up when strangers come in- it raises him up in the pack, increases his anxiety- he doesnt want a promotion he isnt confident enough. never try to settle him with sympathy.

as for neutering some charities offer it free. look up on line. celia hammond do it on discount.