hahahaha yes those frightening ones really are what sort the wheat from the chaff. I had to jump a rainbow once with my old pony, well, 3 times actually because we were in 3 rounds on the day. First two rounds easy peasy, because we'd done a lot of jumping a lot higher and I was riding him REALLY forward into it because many of the other competitors were having trouble with it... and then the third round, the highest, I figured it would be no problem and we very nearly got a refusal.
Goes to show that the only reason he jumped it the first two times was that I was riding him confidently and forward enough that he didn't even see that it was scary.
I might find out who to talk to to get my hands on some old traffic signs to make jump filler with. I have cones but they just aren't scary enough.