Spell Checker in MS word 2003

Hi, I am working as a medical transcriptions. I have encountered a problem with the spell check feature of the MS word 2003 for which I am seeking a solution.

One of MTs have been adding wrong words to the spell checking using add button unknowingly and I have to personally go and delete the wrong words on a daily basis. So, I was wondering if there is any mean or method by which we can disable this "add" button of spell check.