Ugh!!! Love That Collie, a pit bull does NOT lock their jaw that is a myth. Their jaws are strong, they are muscle but they dont lock. I'm sorry but I dont believe some of what you are saying about the pit bulls. I own one, she listens to me VERY well. She does not attack, bite, or try to kill anyone. When people come to my house they are going to be licked to death NOT attacked....

*edit to add*

Please take a look at this link it will you show you the many good things pit bulls can do. From search and rescue to sniffing out drugs.
http://www.pitbullsontheweb.com/petbull/pospress.php