What would you deal with escalating dog aggression?

Well Jack Russel's are Terriers. Terriers are naturally aggressive to other dogs that are bigger than itself! because they are small. Infact alll small dogs wether pure-bred or mixed are all aggressive and BARKERS!, because they all like to make themselves heard and known, they naturally will act out their dominance at a young age and will try and rule all dogs :) its natural, so long as the poor dog as some decent guidance from their owners then it should not be a problem, but still they will bark at their dislikes, unlike their taller cousins who can just walk by and ignore their personal hatreds :)