We shoot on the Gulf Coast beach every once in a while, and our solution has been to use Glad Cling Wrap (prior to that was clear shipping tape - yuck) to wrap around the extension mechanisms. Do this while setting up in a (hopefully) sand-free staging area. What you've likely found as well is that it isn't always the sand you're standing on that mucks up the works, but the sand being blown about.
This does limit your tripod adjustability somewhat, but he cling wrap is pretty flexible stuff. (also helps keep IV lines dry in the shower. Don't ask me how I know...)

A while back I recall B&H selling wooden tripod legs. It's possible they could handle the sand as they appeared to have a simple leg locking mechanism...

You guys have got to be kidding!?

I have shot at the beach roughly weekly for the last 6 or more years. Sure the tripod feet get gritty if they are articulated and the extensions get a little gritty too. You just knock the sand off and in a few days the sand works its way out. When you shoot in the surf, you should rinse the feet/bottom of the tripod off.

This is not an issue.

I simply use a 'Cheaper' Tripod.
The same 'Cheap' Tripod I use for 'Trash the Dress' sessions.
I think it cost me less than $50 at Best Buy and extends up to 6'.
It's lightweight so when I'm shooting at the Beach I simply wiggle the legs a bit to get a good grip into the sand so it doesn't move while shooting. Could use Sandbags but why bring sand to the beach?

The sand is only a problem immediately afterward so I use a travel bag, but as mentioned above, the sand dries & falls off with a little tap or brush off. I guess I could take my 'Expensive' Fluid Head Tripod to the beach but I'd rather travel lite when I'm out in the sun enjoying a day of shooting.

I would be more worried about my Camera Sand, Salt Water, Sea Gulls, etc.

The British Benbo tripod was the best for this, the bottom section was sealed and inverted, so it could go up to some 20" into sand, water, mud or snow. But, while it was an incredibly versatile still camera support, as far as I know, there was never a video version of it made.

Matt I am surprised that with all the knowledgeable folks on this forum that you haven’t been directed to one of these

http://www.myvideo.co.za/channels/xfx

I had to convince my wife the problem was real before I could invest in one and haven’t looked back since

Wow, xfx, I'd have to really convince my wife to let me get one of those... oh, you mean that. ;)

We have very, very fine sand here, so not sure if larger sand is worse or not.

My biggest concern is the salt air, so the first stop when I get home is by the outside watering hose. Open up the tripod (Manfrotto) hose it down really, really well. Let the sun dry it off a bit before putting it away.

No problems at all in 4 years.

xfx, I had been using three, one for each leg of the tripod. You got it down to just one, that's genius!

Well actually I could only afford one that particular model can be very expensive