IMO, tie downs (or standing martingales), or training forks (running martingales) should only be used as a safety device for a horse that flips their head up while ridden (or jumped). It should only come in to play when the horse's head is above the bit, or nearly straight up in the air.
That said, either device shoud only be used as long as it takes to correct the behavior through proper training, bitting, and if needed, saddle fitting and body work (chiro/massage).
I do not agree with the long-term use of these kinds of training devices, nor do I agree with the use of any gadget to "force" any kind of headset, frame, or change in gait. Proper riding/training produces better and longer term results than the use of a quick fix gadget. (proper use of) Side reins on a lunging horse is one thing, to help the horse round and collect without the added interference of a rider, but their prolonged use, the use of tight side reins on the lunge or while riding, or the use of other lunging gadgets is not ultimately beneficial to the horse or it's training IMO/IME.
ETA: I do not know anything about speed events or roping, so I cannot comment on their use there. I am refering to pleasure horses, trail horses, H/J, Dressage, WP, etc. That said, I have seen plenty of good barrel horses run without a tie down, so I am skeptical of their "need" in that event.
Last edited by luvs2ride1979; 12-29-2010 at 12:43 PM.