The ELT is embedded in a foam floatation device. It does, however, need to get free of the hull in the event of an accident as they are normally stowed within the hull space!
fluorescent dye is excellent BUT it is a short term solution as it does disperse very quickly dependant upon sea state, swell and wind.
There is a sonar locator beacon which will activate when submerged. This is normally good for 30+ days dependant upon water temperature and depth. The detection range for this device is also dependant upon depth, salinity and the isothermal properties of the water (layering). Depending upon the sensitivity of the detecting equipment (read the military won't tell you) the detectable range of the sonar locator beacon can be huge.