I just read that you can have a lein put against the non paying parents home when they are in arrears. What if the house is in foreclosure?

If a lien is imposed on a home for nonpayment of child support, the lien is treated like other liens.  If there is a senior mortgage (filed earlier in time) that is foreclosed, the holder of the child support lien will have a chance to pay off the mortgage after the redemption period runs, and own the property, unless a lien junior to the child support lien pays off the child support lien. If the redemption right is not timely exercised, the lien will be extinguished.  The child support debt, of course, does not get extinguished.