I know! I know! I'm so tickled to answer this, makes me think about my filipino momma.
Take the coconut and look for the seam in the middle. Take a towel to put under it and put it on the counter with the seam facing you. Take a hammer an start tapping along the seam and turning it to hit all sides of the seam. My mother would start tapping it a little harder each time as she turned it. The coconut will begin to open at that point you can use a large knife to slide into it and work it open, sliding the knike around the seam. My mom at times used the hammer to tap the knife in to split it open too. You want to be near a sink or bowl to catch the coconut juice coming out. This way you have a perfectly split in half coconut and not have coconut all over the place. You can then score the inside and begin taking the pieces out. I would think if you have a really tough nut you could use the hammer and screw like a chisel too.
Hope this helps!