Heidi usually stops immediately when she want to poo, so there is hardly any time to stop the bike behind her. This time happened what we were always afraid off, i.e. there was not enough time to stop the bike, so Barbara hit Heidi's hind leg with the bike. Heidi moved a bit and pooped on. But from here on it was obvious that Heidi had fear and was not relaxed.
With Chessy it was obvious that we train a little bit wrong, i.e. she stopped every time when we passed certain length of trail - the length of stops was there there with our short training trail. When getting closer to finish line, she blocked a bit (like last time), but we managed to get through the finish line a bit better than last time.
We still need to train more and on longer trails with more turns, but the progress, especially with Chessy, was amazing.