I am searching an area of possible japanese treasure in brackish water, what is the best detector? This concret cach was discovered in 1963, a 15 year old found when spear fishing. and it was 7 feet of water. At present the area is covered with white sand and is only 3 feet when low tide. the area is mark around with signs of engraved line 3" x 20" on coral stone, as a pointer. 2nd an engrave leaves on coral stone measuring 14" dia. pointing to the area of possible concret under brackish wter. what is the best MD to use.