I was taught that bit about holding the line just exactly like a rein by a lady who was a master at lunging. She told me you can squeeze it and soften it and take up pressure and give, just as you would when riding. In fact , the closer lunging your horse gets to riding , the more productive it will be.
What I mean, is not to have your horse come screeching to a halt when you want it to down transition. You wouldn't want to ride that unless you are into reining (no offence, reiners), you want the horse to slow into a balanced stop. You would work for that in your lunging, too.
Transitions upward, you give the horse a bit of warning, like, "AND . . Canter!" and you say it like this, you inhale, and then lower your body a TINY amount as if you are sinking into the saddle for a half halt, and leg on, while saying the "aaaand .." and say it in a rising tone for an upward transition and a falling tone for a downward transtition. Then the "Canter!" can be stronger and clear, and if she doesn't respond in one second, "Canter!!! And reinforce with the whip and don't stop until you get the response. And don't constantly nag her with the whip. If she is cantering, don't even raise the whip unles she DOES break. Let her make the mistake before she is corrected. IF you think she might break you can say , "canter on" in an encouraging tone, but don't ever use the whip unless you are requesting a change. Once you get ther, you let her coast until the next change.
Ok, I am done.
We have about 5 inches of snow on the ground, unusual for around here before thanksggiving.