I had a customer ask me the other day where I preferred to attach my hobbles; high or low. To some extent, this is a matter of personal preference. I like to put my hobbles just above the fetlock (ankle joint), rather than down on the pastern. I haven't seen a lot of chafing when I put them here, not to mention the fact that I don't have to bend over quite as far to put them on! There are some hobbles, especially figure eight and rope hobbles that don't cinch up tightly enough to stay above the joint; just make sure that if you are using these, that they do not chafe or interfere with the flexing at the joint.
On a side note, I also like to have the hobbles up above the fetlock because I can attach both ends of the hobble to one leg while the horse is highlined or tied in camp. Then, should I want to turn the animal out to graze or stop it from pawing, I know exactly where the hobbles are and can hobble quickly. Of course, you should never leave the hobbles attached like this if you are moving down the trail or if you leave the horse unattended.
You can also read my article on training horses and mules to hobble. Just keep in mind that this article assumes that you have a gentle, willing animal to work with. Hobbling a horse or mule before it is mentally ready could be disastrous for both you and the animal.