The best defence is never make yourself too vulnerable. To defend yourself from predators, learn all the in's and out's of setting up a good Safety Net. Follow these procedures religiously. Most important of all TAKE YOUR TIME getting to know your prospective play partners. This is good advice in any case.
Predators are more likely to move on in search of easy prey, they do tend to be impulsive.
If a 'Dom' you have been talking too suddenly seems to loose interest in you after a period of time, you may have just saved your own life. Don't go chasing after anybody. Take the time to figure out what you want. It's often hard for newbie subs to do this because sometimes they lack knowledge of what choices are available to them. Learn about the different types of play and how they should be conducted.