How to avoid memory leaks when using a vector of pointers to dynamically allocated objects in C++?

I'm using a vector of pointers to objects. These objects are derived from a base class, and are being dynamically allocated and stored.

For example, I have something like:

vector<Enemy*> Enemies;

and I'll be deriving from the Enemy class and then dynamically allocating memory for the derived class, like this:

enemies.push_back(new Monster());

What are things I need to be aware of to avoid memory leaks and other problems?