Personally, I would say out loud, with complete conviction, "I take this spell out of the law!" You could add to this with banishing behaviours or herbs if you like, but to me the words would suffice.
If the intent is strong though, I wouldn't worry too much about a detail if it's not vital. It is the energy and the intent that make the magick..If it is a noticable and crucial mistake however, you might take it as a sign that the casting is not a good idea. Perhaps give it some thought and re-assess whether or not you really want to cast this work.
Hope this helps a bit :)