I may have to change my methods once I get a strobe, but for now, my SD550, even in a housing, is small enough that I'm willing to do a giant stride with it tucked up close to me with one hand (to break the worst of the impact). I'll also go through a surf entry like this, on a beach dive.
Once in the water, I have the camera on a very light weight retractor "Gear Keeper" clipped to a D-Ring on the right side (since I'm right handed). The metal cable is plenty strong, but the retractor istelf is not strong enough to hold the camera up on it's own in the air (so I keep it in mand out of the water), but it keeps things close to me in the water no prob, where my cam is only slightly negative, and it doesn't have enough pull to bother me when I'm taking pictures.
Once I get a strobe, I think the rig will be meaty enough that I'll need to have someone pass things down to me. I'll probably stick with the lightweight retractor, however, although I might get creative and get a snap bolt instead of the existing plastic clip... not for strength reasons (remember, there is very little weight on the clip underwater), but so that I can connect and detach it easier, with one hand, and without looking.