There has been a lot of talk lately about being safe in Yoga. To me it is very simple. If we are always practicing Ahimsa, there really should not be any question about being safe.
Practicing Yoga safely should go without saying, but sometimes our competitive nature or ego can get in the way.
The Yoga Sutra's of Patanjali give very clear guidelines for how to practice Yoga and the very first guideline (sutra II:35) is Ahimsa. Ahimsa means non-harm, kindness and should underpin everything we do on the mat and then hopefully flow through to what we do off the mat.
I talk about Ahimsa in every Yoga class I teach. It is the foundation for a meaningful, joyful experience. It is crucial that we are always listening to our body, inquiring into sensations and feelings and making sure that we are working in a way that feels good and healthy in our body.
If your Yoga teacher has you working in such a way that causes you pain, then maybe you should look at whether they are the right Yoga teacher for you. Just as in any profession, there will be a teacher out there who is right for you, it is not one size fits all. There should never be any pain in Yoga.
Recently the New York Times published a controversial article by William J. Broad called "How Yoga Can Wreck Your Body", and I think he raises some good points. But I wouldn't limit it to Yoga. Anything we do where we are not listening to our body when the body is saying "ouch", is potentially wrecking our body. If you are in pain you are not practicing Yoga, or Ahimsa.
Key points for practicing safely
Listen to your own body, your own inner teacher
Find a style of Yoga that is appropriate for you, your lifestyle and your abilities
Find a teacher who understands your goals and respects your body's capabilities
Be brave enough in class to say 'No, that posture doesn't suit me' and don't do it.
Enjoy. Be safe, Practice Ahimsa.