Take your iPhone 4/4S in its Optrix XD4 housing out into the open water with the strongest suction cup mount you can buy.
The strongest suction cup you can buy, the Optrix Super Sucker mount pumps up to over 120 PSI. This mount uses the same technology that allows construction workers to move thousand pound slabs of marble. An orange indicator also alerts users to any loss in pressure before coming detached. Always use safety leash or flotation device when using your Optrix XD in water.