Re training obedience dogs, I've always taught basics with hand signals, the voice command being secondary, so to teach sit, I have a treat in my hand, I raise my index finger above their nose, when they sit I rotate my hand so the muzzle has to go in a downwards motion for them to get it and reward, I use sit as the command, you can introduce down by pointing to the floor and lowering your hand with the dog following. The advantages are, as I see it, you have two ways of command signal and noise, and most importantly, it's a Doddle, to teach th wait command, you just leave the reward longer changing the hand signal to, in our case, a flat palm vertically and use wait in gradually increasing increments.
I used to be able to complete an obedience test without uttering a sound.
You can train a dog to do most anything if you just break down all the movements into small steps and teach them and then reassemble the building blocks in the order you want.
Harry, my last collie, sadly no longer with us, used to be able to complete one of those hoops on a pole kids toys with the rings in the right order, took AGES to teach him, and probably the most rewarding trick I've ever taught a dog, now (he says looking at the current pack of reprobates sleeping on the couch) where did I put that bag of toys......