My dogs have to know 2 things come here and shut up. Other than that they figure out load and get ahead but have switched to a hissing noise for them to get ahead. This works for me. Will say I don't require much handle but they sure better learn come hear and shut up or they don't last long.
Amen!! Shut up is an important term around us too lol.
Our dogs tend to be skittish / don't look for attention (which we like and prefer) but come here and load up are just as important. We can whistle and they come running or shut up (depending on the pitch) and my husband makes some kind of noise to make them go ahead.
We have little puppies that load up in the pens already and dogs that get on the box (they wind) by being told to load up so there is no getting out to make them 'get in'.
Handle is a big deal but it takes time and patience plus knowing what you want.