One way to do this is with workgroups.
It is an expensive price to pay because workgroups are SUCH a pain to maintain, but you can do it like this:
Once the database is secured via a workgroup, go into the
Database Utilities>>User and Group Permissions dialog box.
Now select the database object. There you will find a permission that says Exclusive access. Deny this to everyone except the administrator group.
Now, the trick:
Make sure that the ADMINS user (note the S on the end) is not a member of the ADMIN (without the S) group. Make someone else have that distinction. Like maybe yourself. That way, you can do an open Exclusive but no one else can.
Leave the ADMINS user as a member of the USERS group. But take away that group's Open Exclusive privilege.