How to avoid repeat event binding?

How to avoid repeat event binding?

I have developed a plugin for mutual selection on a list of elements.
It works fine if I make those element into mutual list only once.
like $("appropriateSelector").toMutualSelect();

that plugin will add click event handler to each element and they remember the whole list by enclosure.
If I add new elements to that list. and do $("appropriateSelector").toMutualSelect(); again.
new elements will behave as expected but old ones will have problems.
each old element will have the same handler bind multiple times to them.
that will result like toggle two times and messing up the outcome.

How do I prevent this?
I am trying to clean up their bound handlers but seems no luck.