I had something to say, so I said it, just because you don't like what I said doesn't mean that it was not worth posting...
constructive advice on the real question, your dog is 13 months, has killed on top, I take it with his bull blood he has a very strong jaw and is more than capable of killing a fox.... he is old enough now, if you think he's ready then he's ready, there's only one way to find out.... might jade him a bit if there is a big dog fox in there that latches on to his nose and he cant pull it out... might ruin him, but hey just remember you could have shot the fecker then an