In the meantime, then, I have been doing some studying. I came across this series of two Lucinda Green clinic videos on Horse and Country TV(a UK site). Each of them is a little under half an hour, so they were easily digestible. None of the concepts were brand new to me, but she explains them in a very vivid way.
Lucinda and Regal Realm at the 1984 Olympics. Image: http://www.olympics.org.uk/
In the first episode, Lucinda teaches a group of riders on fairly inexperienced horses. Two of her points were very useful to me. First, cross-country training is about increasing your horse's ability to read and answer progressively harder questions. At first they take a long time to puzzle over a simple question. As time goes by, they are able to process far more difficult questions far more quickly. While Taco is not green by any stretch, it helps me understand what makes him tick. And I also understand my job as presenting him to questions in a way that allows him to solve them correctly (there is that energy, line, balance thing again-- which, by the way, is a concept that Lucinda constantly emphasizes).
Second, she explains that horses initially get up in the air to jump by lifting their front ends. Then the back end propels the horse upward and forward, but it is the lifting of the front end that is the crucial function at the moment of takeoff. So... it is really counterproductive for the rider to allow her body to tip forward onto the horse's front end at that very moment. Again, another concept that I already was aware of, but the way she put it is so commonsensical and crystal-clear.
Here is the first episode itself:
In Episode 2, Lucinda uses two groups of demonstration riders to further explain some important concepts. "Fundamentally," she says at the beginning, "a horse that goes eventing has got to believe that wherever you want him to go, he can go and he's not going to get into trouble." This is exactly how Annika trained Taco, by the way. She always asked him to do things that she knew he could and would do. That is, I am sure, one of the main reasons he is so honest and confident today.
She also has good ways to explain the use of aids. I really liked how she explains the use of the legs in steering and supporting the horse. When steering, our legs are like cling film (Saran Wrap) around a sandwich-- not too loose and baggy, but not squishing the sandwich. Or in my case, not squishing the taco! But then when the horse hesitates before takeoff and/or we're jumping something difficult, those legs can go ahead and squish the sandwich (or taco) in order to make sure the horse keeps going and support during takeoff.
At the end, she works with the riders to put together engine, line and balance over some straightforward gallopy fences.
I'll leave the rest of it for you to discover yourself: