When selecting a marine GPS, prioritize multi-constellation support (GPS, GLONASS, Galileo, and BeiDou) to ensure a stable signal in remote offshore areas. For fishing specifically, look for units with integrated CHIRP sonar technology and high-resolution displays (at least 800x480 pixels) that remain visible under direct sunlight. Ensure the device has a high IPX7 waterproof rating to withstand heavy spray and rain, and verify that it supports NMEA 2000 networking for seamless integration with other onboard electronics like autopilots and AIS.