I'd recommend a citronella collar over the shock type ones. I've seen some dogs get very messed up from the shock ones. The citronella ones give out a spray of citronella or lemon scent every time the dog barks. Dogs generally don't like citrus smells so they will stop barking to avoid it.

I bought Nytron a muzzle called a Husher yesterday. It's a thick elastic, so he can pant and drink with it on. The theory is that the elastic makes it too much work to bark. Too early to say if it will work, but it looks promising.

Of course, as with any training device, you have to be there to make sure it's working. I wouldn't leave any type of collar(besides a normal one) or muzzle on an unsupervised dog.