There are commands that they know are for all of them, "ready boys" is the team and pair command to listen up we are ALL going to do something, like walk off together with no kangaroo petrol involved. Some folk blow a long raspberry that when it finishes the horses know to stop together. I tend to say Aaaaaaand stand. Give them plenty of time to adjust their balance, brake the cart and bring it to a halt on the word "stand"
Rules are for the guidance of wise men and for the strict adherence of fools.