Again, Chokes can be practiced safely. Two types as has already been discussed. Airway and Blood. Airway can be very dangerous if you crush the windpipe, you can also cause it to go into spasms too. So these are not adviseable to practice. Also they are harder to do and do not cause the immediacy you are looking for in a choke. Blood chokes in which you reduce blood flow to the brain are more effective and relatively safe. Note I said reduced blood flow to brain, not stopping it. In reality you only cut off enough to cause them to pass out. It doesn't take much and it doesn't take long.
I practice them all the time with no ill effects whatsoever.
Kevin, what makes your practice "relatively safe"? How do you control the degree to which you reduce the flow of blood to the brain? How do you know that it's "enough" to cause them to pass out and no more? And how does someone learn such things, such that they can practice "safely"? Clearly trial and error is not the way.