Watching with interest...
... and there was me hoping you'd have all the answers! 
lol, nah, mine go spare too.
I do two things that help.
- Every dog is trained to obey 'on the bike' - get on the back of the quad bike and stay there until told to do something different.
- A dog is never sent to sheep when it is other than calm and quiet. (It can be brimming with excitement and coiled like a spring, but it must not be jumping about or yapping)
I could write pages and pages of stories about collie dogs finding their way to work...
Oh, and I have inadvertently trained Dot that her 'get on the bike and stay there' command is the horn. When she was learning, she'd get overexcited when we were gathering big batches, so would get put back on the bike. This was on the moorland farm. I'd be coming behind the sheep, helping the dogs, using the horn to chivvy the sheep if needed. So in Dot's head, a connection was made between the horn and being put on the bike!

Skip of course has the other association, so if I beep the horn, Dot gets on the bike and Skip runs at the sheep!
