How can scientists keep animals from becoming extinct?

The most obvious way of keeping animals from becoming extinct is through the endangered species protection agency. Basically, other countries need to realize that killing off animals for their skin, eggs, etc... does not help populations make a comeback... However, as to scientists, they can obtain DNA samples and flash freeze the samples for whatever time period is necessary. Then, should the scientists wish to "resurrect" the extinct species, a lengthy process must be taken to reproduce these animals. It's basically like cloning animals (It's not that easy).