Thanks JLC! Karma to you, too!
I have to laugh because both you and jackie_w seem to have gone immediately to the Execute SQL tab, where this task was easy as can be, while I spent hours and hours messing with the "Create Trigger" tool, which, from its name, would seem to be the best way to create a trigger -- not!
In any event, I am so very pleased to have learned a few things about SQLite databases and creating triggers. Happy Day!