Users should not be able to access the navigation pane. Perhaps research how to secure an Access db (as much as that is possible). IMO your users table should have a field for user type, not a boolean for management only, then you would not be restricted to only 2 levels should you need more in the future. For forms that are restricted to a particular level, you can DLookup their level during form open event and cancel opening as mentioned. In fact, the form you open could prevent the ability to launch this form entirely, by restricting access to whatever it is you're using to do that (e.g. command buttons disabled or invisible).
The more we hear silence, the more we begin to think about our value in this universe.
Paraphrase of Professor Brian Cox.