no the dogs can't lock as in be firmly locked. they can lock as in not want to let go. the jaw muscles are what powers the jaw bite in any animal. the neck muscles provide back up and allow more damage to be done to tear and shake. as thats what connects the dogs power and weight to the jaws. as i just don't believe the bite power comes from the neck muscle. these types of dogs (pits-bull-mastiffs) have huge fist sized jaw muscles on each side off the jaws. when one has a grip feel the jaw muscle, its hard as a rock. thats whats directly driving the brutes teeth together.(and whats keeping his jaws together when hes hanging from a rope or bigger animal) the rest of the dog provides power to put his weight into his bite. good looking dogs you have glad they have a great owner. oh i have a yellow lab, a pit bull [beeep], a mountain cur, a corgi, a majestic tree hound, a great dane, and a jack russell. they all get along well and i live way out in the country so they have room to run. all but the pit who would run off and attack livestock if i let her loose. so shes walked.- (if you want to believe the neck muscles power the jaws more so than the jaw muscle thats fine with me, but i think your vet means the dog does more damage with his weight behind his bite as all muscle is connected and comes into play when a dog is fighting and has a grip working it with his entire body- oh and when you bite something do you feel your jaw muscles powering your bite?) /ubbthreads/images/graemlins/grin.gif