The safest way is one year at a time (8332 part I) and provide a new form each year. It takes a full year to revoke a 8332 (part II) future years. In other words, if something comes up and you want to revoke it, the revoke will not happen for year *after* the year that you submit part III.
Note that the 8332 only applies to the dependent and child tax credit, The EIC and child care credit is tied to physical custody (the parent where the child actually lived more than half the year) - those can never be claimed by the non-custodial parent.
**Disclaimer: This post is for discussion purposes only and is NOT tax advice. The author takes no responsibility for the accuracy of any information in this post.**