How can I get around this problem?

I have an application that needs to perform a lookup on a table contained in a DBC other than the DBC that I use for the app. My logic to open/close that table is as follows:

USE table SHARED IN 0 ALIAS mytable
...
...
IF USED("mytable")
USE IN mytable
ENDIF

As you can image, at this point I am assuming that this lookup table has been closed. However, it appears that its parent DBC remains open and therefore creates contention for other users or apps.

1. How come USE IN does not close the DBC the way it opened it?
2. How can I make sure that I close the table and DBC?

Thank you,