"to derail a train of thought".
Another one of those which falls into the category of "probably coined by multiple people". Google has a number of links to the the phrase. I cannot claim to be the originator of this one. Again, another colour piece of English usage.
“can’t stop the merry-go-round to paint the horses”
Another one of those picturesque phrases. This is probably unique, Google does not find it as a phrase. Again, I cannot claim to have coined this one.