I wouldn't think to tell you what your thesis should be. However, i do believe that if you can inform yourself well on the topic, you might be better equipped to decide what you will write about. So i recommend that you click on the link below, which will provide you lots of information on dog bites:
Dog Bite Law
The site is maintained by a personal injury lawyer in Los Angeles. Not only does he provide a lot of information--on the home page is a link which is entitled "Links" which will help you find a lot more information.
So, for example, he has information which confirms BDoug's contention that although rottweilers and pitbulls are implicated overwhelmingly in fatal dog attacks, they are much less likely to attack than other breeds.
Good luck.