In a lot of cases you won't need a zapper. A citronella will do just fine.

There are some things to consider though. Two weeks previous to actually use the collar get the battery out and replace it with something just as heavy and stuff it in their using cottonballs. It needs to be just as heavy so the dog can't feel the difference.

In those two weeks the dog has no bad experiences and therefore doesn't link the collar to being spraid. After that use the collar untill the dog stops barking for about another two weeks.

In future you let him sometimes wear this collar activated and not activated or even another collar. After sometime they don't need them at all.