You might also consider using $dbh->quote() to quote the strings you are inserting into your SQL statement.

Even better: Don't quote at all and use placeholders instead, especially when the SQL statement is executed repeatedly. That way, DBI and the database can cache a lot of the work that has to be repeated when not using placeholders. See Re: Counting rows Sqlite, Re^2: Massive Memory Leak, and of course the DBI documentation.

Alexander