A question about ORA-00054

I had a quick question for a intro DB class that I am teaching, and using Oracle.

My students some times run into this problem --

They perform a DDL statement, say drop table in one session. They then lose the internet connection or something happens. So somehow it ends up locking the table.

Then restart their client and try to perform the same DDL operation -- it comes back with a ORA-00054 error message, and they cannot continue. I think they wait for one hour or so before the lock is released.

My question is -- how do I specify a duration for the lock? probably I can specify it for the entire database for all users for all their DDL operations?
or is there a way of specifying for each DDL (or can even be DML) statements, the duration to hold the lock..?

Note: students who are getting the ORA-00054 operation, I do not want to give them SYS privileges.
Just to inform you, if things work normally, the drop table should finish in a couple of seconds.

Remember I said this is for a class. So some students end up dropping the table and creating it again multiple times (because I give the scripts to create tables and populating data).

again, I was wondering if there is some way as an administrator, I can set up so that the locks will not persist for a long time, and I do not get email from students saying -- their create table is giving them ORA-00054 error..
can I change the lock duration?? I was looking up -- http://www.morganslibrary.com/reference/startup_parms.html -- I could not seem to find what parameter I can set up??

Or is there a script that I can ask students to use for dropping a table, so that it locks only for a short duration..

thanks, murali.

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