My 6 month old Olde English Bulldogge has been getting increasingly aggressive whilst out out walks. It mostly manifests itself as barking but if he's off his lead in a field, he will start tearing around snapping at the grass and then trying to nip my ankles. I don't know if this is his herding instinct? It's definitely much worse when he's in a field or open area - if we are on a path he generally trots along happily at my feet & it all seems completely out of character as he's good natured and reasonably obedient at home. Things I have tried with limited success are: 1) Put him on a tight lead every time he starts off and let him off again after 100 steps. This works eventually but it's always back to square one on the next walk and I have to go through it all again. 2) Stop dead for a few minutes, ignore him, turn my back on him. This shuts him up too but he soon starts again once I start walking though eventually he does stop. I don't know if this is herding instinct but I've read various posts on other sites about rewarding him when he's good and I'm doing all those things too but this isn't getting any better and he'll soon be a big dog with powerful jaws so I'm somewhat worried!