While the handheld is a quick and dirty way as well as having the versatility of taking it with you, its not something I would want to take a chance on. I view the VHF radio as being as important as the PFD's or life ring I have on board.
I don't know if you have a cuddy, or a bow rider, but either can accomodate one of todays radios. Check out the following web page:
http://sempreveloce.tripod.com/index.html
Notice that I have the antenna mounted on the Port side. If you take care and use a fold down mount, you will be able to have the antenna fold down and rest on a cleat. Mine folds forward. a rubber band holds it in place as I motor down the road.
I can relate two seperate emergency situations that happened to friends last year, and in each case had they not had a radio on board, the whole family would have been floating in the river as their boat's sank. I'm not trying to scare you, but you know the old saying "How long can you tread water?"
KKKKFL