You can terminate a user with KILL. Look up the KILL statement in SQL Server
Books Online. But that should be the last resort. It's better to find out why
the users were doing and perhaps a procedure change is in order.

Linchi

Yes, you can do just about anything you want in a Trigger. Yes, see why they
are doing this before cutting them off. My first question would be, however,
why do they have direct table access?

It sounds like more of a security and/or declarative data integrity issue.

#1 Do not grant access to users who don't need it. If an unwanted user has
access to the database due to their windows group membership, then instead
only grant access to specific accounts or deny access to specific accounts as
needed.
#2 Implement a primary key that would prohibit inserting duplicate data.
#3 Implement stored procedures to perform the inserts which includes
additional logic to prevent inserting unneeded data.
#4 Rather than granting users insert / update / delete permission, instead
grant them execute permission on the specific stored procedures they need.