Have done this to a mate in the past. Will definitely do this to my slave
This is a great dichotomy between Owner and property.
The slave could already be trained to behave like this, or undergoing training. I suspect if the slave is training it will take a while for the slave to get used to the cold and the wet conditions. That said, walking naked like this while ensuring his Master stays dry is a good lesson to learn, and does illustrate who has the higher status in the relationship, and rightly so.
After this the squirming slave will submit totally. The slave is secure, cannot see what is happening, but he knows feeling the force of the whip on its penis is a means of punishment to instil a lesson for shoddy work, and also trains the slave to accept and take pain as a means of punishment during his training during each stage of his development.
Good to see a smooth hairless slave, in his rightful position!