dont forget that you also get hard dogs without any bull in them, i know a fela and he had little border crosses,they wernt much bigger than a rabbit but they were mental,too hard for there own good.it comes down to what stuff is in them,bull or not.
I have a bitch who is 10ins to the shoulder patt x russell and she is the finder, the digger she only does rabbits and rats not like you guys but she is the toughest of all my 7 terriers and is deffo the boss lol.. No bull in her