Track Changes is a toggle. It may be off, but someone can turn it back on. Even if it is turned off in normal.dot, it can easily be turned on in any document.
If you don't want it on, don't turn it on. If you mean permanently disable it from BEING turned on, you could remove it from the menu. However, if someone wanted to get it back on the menu, it would not be hard to do so.
Gerry