It's interesting that terrain running is a focus. It makes so much sense and yet I've rarely heard of any training in the US that focuses on just running in the terrain separate from running courses in the terrain. It might be there, but I've never heard it mentioned.
I think ARK does this well and it's probably something that should get added to US training camps if it's not already there.
Absolutely. Clubs or school groups with limited access to mapped terrain could do lots of activities that improve both general and orienteering-specific fitness. All you need is a small patch of woods, doesn't even have to be mapped. It's great for their orienteering development and, more importantly, it's fun!
I have tried to get terrain runs in regularly, especially in parks I know pretty well. It's lots of fun and no pressure to find anything (except your car at the end). And of course good specificity training.
I've done these from time to time, very useful. Get in the woods, pick a direction, run for a period - 2,3,4 minutes or whatever, recover, turn around and go back for same time. Repeat as often as desired. It's great for getting used to running in terrain without having to try to read a map and figure location. Ignore that as you will be coming back to the same place, supposedly.
Around here I sometimes just run parallel to a trail, or weave around a bit, to get in some terrain. You really don't have to think too much to do that.
Terrain intervals also make it easier for a group with varied fitness to train together. The lead runs a zig zag or figure eight or something with lots of turning back so that those who are behind can cut corners and keep the front in sight.
hashing is great terrain running training and also good for letting slower runners catch up. I've used a version with kids sans the foul language and alcohol that usually accompanies most adult hash runs.
That's a great idea for a game that is secretly training.
For intervals - usually 70/20 - terrain running in even a larger group is very good training. You just keep 'circling around' and catch/meet the rest of the group to basically reassemble at the start of every 2nd or 3rd interval or so.