There's a simple way to prevent user's from getting behind the scenes to the tables.
See this example. Note that the mdb first opens a 'mainformbackground' which maximizes and then opens the popup main menu form. This prevents users from accessing the upper main menus to close any forms.
http://www.dbforums.com/6332819-post68.html
Although this doesn't prevent holding the shift key and opening the mdb/accdb to get behind the scenes (and I wouldn't recommend any coding to disable this), most user's don't know the trick of holding the shift key down while opening the mdb.
Also create an mde/accde versus using an mdb/accdb. This prevents user's from seeing the code should it bomb out anywhere or getting into design view.