Pearlsasinger
Up in the clouds
Sis & I hack together frequently. We will often say to each other e.g. 'let's trot to/from 40 sign'. No matter which of them is in front they will both start/stop as the front one reaches the sign. I should add that we make a point of not having trotting/cantering places, so it's not that they know where we do particular things, they must understand/pick up what we mean.