1a. To order someone to go away or "get lost." This is a widely used term that has no vulgar connotations.
One friend told another to pound sand when he questioned the veracity of the Old English Dictionary.
1b. Walk away (from the fact that each step requires one to press down the sand beneith one's feet; from Hawaiin slang)
Go pound sand.
2. "The origin of the expression go pound sand is from a longer expression, not to know (have enough sense to) pound sand down a rathole. Filling rat holes with sand is menial work, and telling someone to pound sand down a hole is like telling them to go fly a kite. The expression dates to at least 1912 and is common in the midwestern United States."
3. The term pound sand originally referred to the degrading job of filling rat holes with sand. However, its meaning has evolved, it now refers to a technique used in Vietnamese whore houses. This technique was used when the whores would give a man a hand job and then right before the man would ejaculate the whore would cap the penis, give it one hard pump, and then release it causing the man to ejaculate with such force that the it would hit the ceiling.
Hey, why don't you go pound sand!