How can I keep my current relationship healthy while forced to deal with a toxic ex?

My ex-husband is a very unhappy man. We have been divorced over a year and a half and rather than making any attempt to move on with his life, he seems to have focused all of his attention on blaming me for the break-up and thinking of ways to hurt me. Because we have children together I am necessarily tied to him until my youngest reaches the age of majority – eleven more years. Of course his weapons of choice, because they are easy and available, are the children. I have a pretty good handle on how to protect them and keep focused on what is best for the children. While my man and I are totally committed to one another and to riding this out, I am interested in hearing from those who may have been through something similar – or anyone who might have some helpful thoughts on the subject. I am wondering what steps I can take to protect my current relationship while living with the inevitable stress an angry, vengeful ex might cause.