Yes, corrosion is a big issue. Metals and other materials used in the robot's construction can corrode when exposed to saltwater or other chemicals in the water. Special coatings or alloys are often required to mitigate this.

Are there any common challenges or issues with these methods?

Coating methods involve applying a waterproof coating or film to the robot's exterior. This provides a barrier against water ingress. However, the coating must be durable enough to withstand abrasion and long-term immersion in water.

Interesting. What about coating?

Pressure compensation systems allow the robot's internal components to adjust to the changing external pressure as it dives deeper. This prevents the components from being damaged due to pressure differences. The challenge here is designing a robust system that can handle extreme pressure changes.