Below is an ad I found in an old Forum program to fill you in even more. You can see at the bottom how to order the plastic shields, which cost a buck.
The problem with the shields, though, is that many of the coins fell out too easily. This became a nation wide issue for young boys, and often the coins were glued in. And because it happened so often and most were like this, the glue has never really taken away from the value of these sets.