yes, I have I've also had ago with a shock collar and one thats used on a dog for the invisible fencing see no reason why a dog should have to do something I am not prepared to try myself first
Working dogs that have to go through sheep are absolutely useless for their job if you can't let them off the lead... again I would say only in an emergency and as a last resort. I'm not a trainer and certainly wouldn't put myself out there as one but if its the difference between life and death or being rehomed then I would in an emergency use a method that is prehaps not driven by chucking sweets. Prey drive is alot stronger than the need for food reward in some dogs.
I'm always happy to re-educated if you have a better method... and please don't chuck cesar milan at me I don't use his methods of flattening a dog either.
Get a dog that is not so hard wired and train it to be steady then.
I agree that often manmade reinforcer's cannot compete with the animals natural instincts but these instincts and their strength vary from dog to dog.
Some dogs are just too hard wired to work where you want, so do you find a dog that you can work with or punish the hell out of the one you already have?
Some working dogs are not fit for purpose, people just have to get their heads round that!
I don't think the original post referred to a working dog in an emergency situation so where spray collars comes into it I don't know.
edited to add
Don't forget a dogs prey drive if strong enough could override any punishment dolled out.
there is also spontaneous recovery of a behaviour you had previously thought extinguished. What then do you keep on punishing?
Sorry but IMHO it is a slippery slope to start down.
Mark