The best deterrent I have found is the use of a silver security label that is
placed over the seam of the case. It has some language on it that says
that if this label is tampered with, the patron is liable for the entire cost of
the tape. When removed, the label leaves behind silver that says *VOID*.
I have found these very effective. They can also be custom made with
your library's name, etc.
In addition, you must train your staff to carefully look at every video tape
before discharging it. With the silver label, it is very simple to see when it
has been tampered with and a patron's record can be flagged
immediately when a tape is returned. Staff training is really the best
Non-Print Materials Evaluator
County of Los Angeles Public Library