Engine Coolant Leak?

The engine coolant will leak out on the bottom of my expedition when I turn the car off. It has overheated once in the red and engine was about to stall when I discovered the problem. What is the best way to check what this would be?

Thanks for your help

You can get under it and see where the leak is starting from. If you can get a pressure tester and have the system pressure tested, the leak will show quickly.