Cataholic these collars don't really cause pain, more of a buzz. if the dog then continues the buzz gets a bit stronger but most dogs only need to feel it once or twice and they get the message. I got mine at PetSmart and I know that if anything at all is bought there they will take it back no matter the reason. one thing I do like about then.
But, saying this, I would never ever leave a dog alone with a shock collar n, thy aren't meant to be left on for long unsupervised periods. I've also heard of the ones where you hold the control in your hand and use it mostly when running the dog loose on fields but hose shouldn't be used as bark collars IMO.
If bark collars seem too barbaric then you can buy a monitor that you leave on a table , when the dog barks it activates the monitor and the dog hears an unpleasant sound so he can't associate it with anything or anyone, just his own barking since that's the only thing that sets it off. By the way, no one else hears a sound, which is very nice.
Beagles are a bit different but I've seen many people using bark collars on them without ill effects.
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