Is it permissible to raise dogs to train them for guarding, and then rent or sell them to perform guarding duties?

The Shari'ah has prohibited the acquisition and sale of dogs, but it has permitted the acquisition of hunting dogs, livestock dogs, and farming dogs, as well as dogs for urgent needs such as guarding homes. The reward of anyone who acquires a dog for purposes other than these is diminished by one Qirat each day. As for the price of a dog, it is forbidden, and its sale is invalid, and this includes guard and hunting dogs.