Fielding Chase gets a gun from the trunk and is going to shoot when the cyclists arrive. Dr. Eric Mason sics the dogs on him with Rosebud. I can't think of any more. By the way, what does the title Butterfly In Shades of Grey mean?
I just watched the Fielding Chase one again and I noticed that earlier in the episode, Columbo mentions that he doesn't carry a gun, and Feilding says "interesting, I'll have to make a note of that..."
As rare as attempting to murder Columbo is during the series, it did occur three times within five episodes along the timeline (Murder Under Glass, How to Dial a Murder, Columbo Goes to the Guillotine).