Bogged in sand.

I've heard this practice can be dangerous as the anchor can leap out of the sand under load whereas a proper ground anchor is designed to keep digging itself in under load.
I've only heard this but I do query it as I thought a plough anchor also did that, just a less technologically advanced (and therefore cheaper) design.
Another possibility is these anchors were not designed to take such loads, unless of course you get a real big one which will then cost about the same as a true ground anchor and be a lot heavier.
I'd like to hear more reports on the subject.

Sea anchors only work properly when the stem of the anchor is weighed down on the sea bed by a heavy length of chain thus keeping the nose or point digging into the sea bed but not burying itself. If you have a really muddy sea bottom you really need a heap of chain.
So, this all seems a bit useless, especially if you have soft dry sand.
Carpets a crook idea, it's bulky and stinks when it gets wet.

Willies suggestions are spot on but I'll add another 2 cents worth.
I like to multi-task anything I take on a trip, if possible. If a bull bag looks like it might press into sharp edges use an old corn sack or cloths, bedding etc to protect the bag from the sharpies.
Best multi extra we carry is a couple of big sheets of Sarlon (shade cloth). Its tough, water resistant, light. Can be carried up on the roof rack, used as a hammock and for collecting timber on.
Best use is on ground under tent (protects base and stops sweating) and as a large mat out in front to keep tent interior clean ( the bigger the better) - now if you get bogged or look like getting bogged, guess what's getting dragged down off the roof rack - the big sand mat. It works.