Styrofoam tombstones come with little spikes the size of toothpicks that inevitably break, but the styrofoam isn't big enough to drive anything more sturdy through it. I needed something that could be affixed to the back of the tombstone without puncturing it, with a large surface area to account for the relative flimsiness of the styrofoam. So I made these. 

They're sized to hold a 10mm yard stake but they can be sized up to hold stakes of any size. 

Print in an upright position so that the first layer has a P shape. Printing the bracket flat on its back will result in less adhesion between the bracket and the plate.