problem: users can still change font and size of text in TEXT box

question: how can I lock up the ability of users to edit the font type size etc. inside a TEXT box (inserted from the CONTROLS section)?

background: I am making up a word 2007 document form and I am including some editable text boxes for staff to fill in. I have been using the menu and selections of: DEVELOPER-CONTROLS-TEXT. Everything has worked well so far but when I test it out I find that I am able to change to text size/font. i want this to be the same on all completed documents without staff tampering/altering this feature.