The two Doberman's I've owned have actually been the most placid and docile dogs ever they're more playful than anything great watchdogs though, I can't speak for boys since I've only ever owned girls and they are the sweetest things she even eats next to the chooks and shares their food sometimes even though she's not supposed to lol I'll attach a pic
I think what I'll do is make a run and fox proof it as much as possible and keep them there most of the time, and just let them have the free run of the yard for a couple of hours a day then return them to the run, my dog will be outside with them alot of the day too and she would probably scare a fox away (by trying to go play with it )