I'm always interested in hearing how to best support strength and suppleness in my older horse, so I went out and bought a book on equine fitness. It's a great book, but probably 75% of the exercises are identical to the work my horse does on our local trails (which can be alittle rough, as the town is not exactly into trail maintenance).
I'm not going to stand in the ring and use a longe whip to get her to lift her hind legs when we can go ride a trail that has alot of small blowdowns to step over. :-)
Just another reason I get to insist on boarding where there are trails. :-) I feel fortunate to have that option in this area; I know that it's getting harder and harder to find, in general.
I also board at a nice facility(100 acres, plus permission to ride on several neighboring properties). There is a nice ring with jumps, a very basic grass dressage ring, and some cross country jumps plus alot of trails. My mare(17 yo TB) and I get tired of schooling in the ring and usually trail ride at least a couple of times per week. Way more fun then working in the ring...