mate I don't like the thought of using them and I haven't as yet but all of the keepers I know use an electric collar, One of the lads who has a very good rep for breeding long dogs swears by them for kennel noise.
On the plus side I did try one strapped to my arm and on full power it felt like touching a not so strong electric fence. I have been tempted to use one on my little kelpie cross lurcher as she hates horses and we live in a horse area, but so far ive avoided it.