Hacks are great, and I think people don't realize how much pressure it really really takes to make one dangerous, short of leaning back with all your weight on a hack I don't think you can damage your horse, and if you are watching your horses reaction it should never lead to that dilema. I ride on contact with a hack, though my hands are stable and subtle, and I like it when schooling a horse that lugs on you during halts, or needs a refersher course on what whoa means. The type of pressure that could cause serious damage with a hack is the kind you wouldn't want to use with a bit, or anything, short of a halter.
Troubled TB ~"A thorn by any other name will prick just as deep." @-'--,---