reference counting and garbage collection

I read something today from someone else's source that made me think. He said that since PHP uses reference counters, you need to 'unset' all your references before you exit your script. In particular, he was talking about an n-ary tree data structure he had made. He insisted in his comments that before the script ends, you call his cleanup method that goes through the entire tree and 'unset's all the references to parents and children. I'm worried about this, because I wrote an n-ary tree data structure as a navigation hierarchy for my website <http://www.apt7.com/src/NavNode.txt>. It uses references to keep track of its parent and its children. Do I need to unset these before script execution ends? Will I end up with memory leaks? I'm not familiar enough with the innards of PHP to know. Thanks to any brave enough to tackle this. Dean.