Here's a great counter to the heel kick. This move is actually inside Tai Ji Quan forms, but I adopted into my Mantis Boxing system after seeing it in Muay Thai and realizing what it was. It's an awesome counter/defense against the heel kick, and definitely one I want in my arsenal.
There are some nuances to it, and inside this video I'll highlight 3 fail points that are common and how to avoid them. Check it out.