What is the ruling on working in dog training?

It is not permissible to train dogs or keep them except out of necessity (such as for hunting, guarding livestock and crops, or detecting crimes). Whoever keeps a dog for reasons other than these will have a qirat deducted from their good deeds every day, due to the Prophet's (peace be upon him) saying: "Whoever keeps a dog, except a dog for herding or a dog for hunting, will have a qirat deducted from his good deeds every day."