What are the signs?

I live in central Mindanao where there use to be a Japanese army WWII camp of some kind. My future father in-law over 40 years ago excavated this property for stone crushing purposes. In one portion of the property he dug down about 4 meters and decided to grow banana there. One banana tree leaves were always turning yellow so they dug it up and hit a big rock. After uncovering the rock, a round circle with Japanese writings was found on the top center of the rock. The marking was sheared off so I can't tell you what was there. It's been too long ago for anyone here to remember what it looked like. Now I come along and decide to build a house with a basement. Guess what happened to be in my way? After digging 3 meters down we hit another very large rock. We have decided our best approach with that rock is to dig a deep hole and push it in. Back to the first rock. This rock we decided to remove with a jackhammer. It is an interesting rock. Seems to made up of all kinds of interesting looking stone, lava rock and different colors. Some say it is man made. I have read that those that buried treasure during the war marked large stones to show there is treasure in the area or under the rock that is marked. I have also learned that many of these treasures were booby trapped. In another section of the property while digging out an area for a fish pond we did find an unexploded ordnance.
Anyone here have any other information pertaining to this kind of find? Anyone have information on sites that may show these kinds of rocks or if the Japanese did make rocks to cover treasures? Any information on factories, bases or plants of any kind (ice houses, farms) or anything of the kind controlled by Japanese armies in Mindanao?
Thanks for your help.