Well I got a number of PMs from different people regarding how I managed to shoot some seascape waves and do multiple exposures without the tripod being knocked over, moved or sunken to the ground, caused by the splashing and hitting from the waves. Hopefully, this Behind the scene shot will answer your doubts.

Here's an example from Labrador. I like the compo but I couldn't find a rock to stable my tripod, so I had to do this the hard way. The beach at Labrador has got to be one of the strongest tides and waves in Singapore in my opinion.
Warning: Doing this *might* damage your tripod and increase wear and tear, especially if you're not careful. Or if your tripod is known to be flimsy and not too stable, I highly suggest not to try this if you're concerned about damaging it.
And here's the trick (Closeup Right side):
Just slide open the last legs of your tripod (Warning: Don't expose the levers to the sand/ground!!) and bury it deep into the ground. Bury each of the legs deep into the sand until you can't push any further in. And that's where you have found your safe and stable depth. =) Right hand on the shutter, left hand on the center column. Don't grip the center column tight but rather hold onto it and give a gentle downward pull, as though giving the effect of weight. This adds "weight" and your hands help to further stabilize and detect any movement from the force of the waves.
There will be some scratches to the rubber soles but that can be exchanged easily. And I believe good ones should last. I would prefer the metallic spikes but there aren't available for my tripod.
PS, after shooting it's always advisable to wash your tripod that was exposed to the sand. Many of the beaches here have wash areas near the public toilets, so those come in handy. A rag or a cloth to clean its legs should be great too. Disassemble your tripod and clean the insides if you must (I do that too a couple of times when needed).
Well, this is my own sharing method of shooting the waves. Hope this helps!