Your case seems to ring a bell. I've encountered that before, although mine was smaller and not turtle shaped. Mine was triangle-shaped rock and at one side of that rock was placed another black bulging stone as big as a man's head. It is actually a pointer - pointing to the load. That stone was in the middle of a river, about 10 meters from the load. (Our digger broke it, and surprise! nothing there!!). About 100 meters away was a pink turtle with head also pointing to the direction of the load but had a drawing on its back on the placement of the loads. Markers like that clarifies and strengthens your position. So never, ever break it unless you are 101% sure there's something inside because you will go back to it later several times for clarification.
Voyager