Hi Steffi
Last week we did some barrel racing in the arena at Erikas place. I can't tell you if it does harm the canter as Dancer is not yet that far but what I definitely know it is soooo much fun!

The second time we did it Dancer already knew when to give speed and he enjoyed it a lot. After that I was working him in his galopp and I could not feel that he would want to start racing. He was just listening to my riding signals and those told him that the race is over now and he accepted.
If you look at reining horses those also must differentiate between lope and very fast galopp and have no problem with it. I think it is a training issue.