That is just one of the aggravating things about this case. In my hometown it is so bad that my wife is afraid to walk our two dogs (German Shepherd and mutt) outside our immediate neighborhood. There are platoons of teenage boys from the 'hood walking their untrained pit bulls on chains attached to harnesses. (That means they are not under control.) We have heard of a number of dogs that have been mauled around town. I've taken to carrying a pocket knife with me in case one of these dogs clamps on to one of mine. You can't get them off otherwise.
I got news for you. A pocket knife is useless on all but the tamest of pits, and those you don’t need to worry about. These dogs don’t feel pain. Get yourself a stun gun. When they are locked onto your dog, you will be zapping the both of them, but at least the pit will be disabled long enough for you to get your dog away. If he revives, zap him again. If the owner attacks, zap him too.
I personally believe in bullets and guns, so I don’t bother with the other nonsense. No knives, stunguns, or pepperspray for me...just hot lead moving real fast.