To be prepared is the only way you can keep yourself out of harms way. You might think that a can of mace will be able to do that but if you dont have time to take it out, then it is useless. This is why you have to learn Jiu Jitsu.
Jiu Jitsu is an ancient Japanese martial art. It is technique which consists of ground grappling, punches, kicks, throws and weapons. The key here is leverage so even someone small will be able to learn it.
If you think defending yourself is the only benefit of learning Jiu Jitsu, think again. Studies have shown that learning a martial art like this one will help build balance and coordination, increase your self-confidence and self-discipline, improve mental focus as well as reduce stress.
It is also a great form of exercise that will significantly improve your endurance, flexibility, muscle tone, speed and strength since you are doing this repeatedly to get the technique right.
You can also learn Jiu Jitsu to attain fame and fortune. You will have to learn this technique first and become an expert just like Royce Gracie who used this technique to win the first four championship titles of the UFC or Ultimate Fighting...