You can prevent them looking at the design of your form, by creating a MDE
(more on that below). For some simple measures there are a number of things
you can do:
Backup your database; you can easily lock yourself out playing around with
these features.
Create custom menus/toolbars for use throughout your application.
Create a startup form (a main menu form if you have one) that is opened on
startup.
Use the features in Tools, Startup to
set the startup form
set your default menu (the custom one you made)
disable all the checkboxes about allowing built in menus, toolbars,
changes etc.
hide the db window (ensure the custom menu you create does not
include the Windows, Unhide item)
Uncheck the allow special keys (this will disable the F11 key, among
others)
If you need to bypass these startup features, you can hold the shift key
down while you open the db. If you feel that your users may use this to
bypass your settings, you can disable the shift key bypass - there's an
example in help for doing this(look for AllowBypassKey) or at
http://www.mvps.org/access/modules/mdl0011.htm
and
http://www.mvps.org/access/general/gen0040.htm
You can also create a MDE from your database, which will prevent changes to
forms, reports and modules (If you do this, be certain to keep your original
mdb in case you need to make changes).
None of this will keep the determined out. All they need to do is start a
new db and link to your's, but this may suffice for your purposes.