you could set the properties of the BE file , and remove all his rights.
But if he still needs to use it, AND he knows the path to the backend, I dont know how you stop him besides tattling.
I have a table ,tUsers , of those allowed in. When the app starts, it checks the list to see if they can be in.
If so, i Hide the tables.
DoCmd.SelectObject acTable, , True
DoCmd.RunCommand acCmdWindowHide
of course this could be byPassed with the shift key if they know that trick,
so then you must disable that!