1) Submerge yourself in water. Make sure it is Above your head.

2) Don't move.

1) Make a hole just big enough for your character, then make it deep enough so you can just barely jump out.

2) Jump out and cover hole with one block thick block things.

3) Place enough sand above hole to fill it.

4) get back into hole from side and fix it to make sure it only has the room to fit you.

5) Break the two blocks covering hole.

5) Profit.